WO2005021954A1

WO2005021954A1 - Valve

Info

Publication number: WO2005021954A1
Application number: PCT/GB2004/050003
Authority: WO
Inventors: Thomas Wielkopolski
Original assignee: Cooper-Standard Automotive Uk Fluid Systems Limited
Priority date: 2003-08-29
Filing date: 2004-08-20
Publication date: 2005-03-10
Also published as: EP1664518A1; GB0320335D0

Abstract

An exhaust gas recirculation valve (2) for use with an internal combustion engine for an automotive vehicle, the valve (2) comprising a passageway (6), a closing member (10) that is movable between a closed position and an open position which allows fluid communication through the passageway (6), and an actuator for moving the closing member (10) between its closed and open positions. The actuator includes a driver (26) that in use causes movement of moving parts one of which causes movement of the closing member (10) to the closed position, after which continued operation of the driver moves a second moving part (22). When the driver is operated to open the valve, the second moving part (22) moves back to its previous position and the momentum of this movement assists the movement of the closing member (10) from its closed position to its open position.

Description

Valve

The present invention relates to valves and in particular to exhaust gas recirculation valves for use with an internal combustion engine for an automotive vehicle. Exhaust gas recirculation valves operate in harsh conditions and should not only be able to withstand repeated operation in such conditions, but must also be able to continue operating effectively over prolonged use. Possible problems that can occur include sticking of the valve as a result of the build up of deposits from the exhaust gases and limited lifetime. Also, certain valves of the prior art lack the ability to control effectively the operation of the valve. It is an object of the present invention to provide an exhaust gas valve that mitigates one or more of the above- mentioned possible problems. There is provided in accordance with a first aspect of the invention an exhaust gas recirculation valve for use with an internal combustion engine for an automotive vehicle, the valve comprising a) a passageway, b) a closing member that is movable between a closed position in which the closing member closes the passageway and an open position which allows fluid communication through the passageway, and c) an actuator for moving the closing member between its closed and open positions, the actuator including i) a first moving part that in use causes movement of the closing member, ii) a second moving part, and iii) a driver that in use causes movement of the first and second moving parts, wherein the actuator is so arranged that in use: at the instant at which the closing member reaches the closed position from the open position as a result of the driver being operated to move the first moving part, the second moving part is at a first position, and thereafter on continued operation of the driver the second moving part moves from the first position to a second position, and when the second moving part is in the second position, the closing member is in the closed position, and the driver is operated to open the valve, the second moving part moves from its second position to its first position, at which position it has kinetic energy that assists movement of the closing member from its closed position to its open position. Thus the opening of the valve may be assisted by means of the momentum of a part that is moving at the instant at which the valve closing member is to be moved from its closed position. It is known to provide a valve, wherein the opening of the valve is assisted by means of a hammer action of some sort provided by a drive means different from the drive means for operating the rest of the valve movement. One such known valve is in the form of a poppet valve that includes a wedge shaped member that is moved by a first drive means in a direction perpendicular to the valve before the valve is opened. The wedge hits a member connected to the poppet that partially lifts the poppet from the valve seat and thereby "breaks the seal". Thereafter the poppet is lifted by a separate second drive means. Such a valve has many moving parts and suffers from the disadvantage that two prime movers are provided. In contrast, the present invention is able to provide a valve that has relatively few moving parts and requires only one prime mover, as the valve may be operated by one and the same driver. It is furthermore believed that valves according to the present invention will prove to be generally more reliable than valves of the prior art designed for the same purpose. The actuator is advantageously so arranged that, in use, in the event that the closing member becomes stuck during movement between its closed position and its open position, continued operation of the driver in a direction that would normally move the closing member towards its closed position causes the second moving part to move from its first position to its second position. Similarly, the actuator may be so arranged that in use in the event that the closing member becomes stuck during movement between its closed position and its open position, continued operation of the driver in a direction that would normally move the closing member towards its open position causes the second moving part to move from its first position to a third position, the first position being between the second and third positions . The valve is preferably so arranged that in the event that the closing member becomes stuck during movement between its closed position and its open position, the second moving part may be moved by the driver from its first position to another position and then moved back to its first position, so that when moved back to its first position it has kinetic energy that assists movement of the closing member from its stuck position. In the event that the closing member is stuck and is to be moved towards its open position, said another position may be the second position (so that the driver operates in a

• direction that would normally move the closing member towards its closed position so as to cause the second moving part to move from its first position to its second position and thereafter the driver operates in a direction that would normally move the closing member towards its open position so as to cause the second moving part to move from its second position to its first position) . In the event that the closing member is to be moved towards its closed position, said another position may be the third position. In the event that the valve is arranged such that the second moving part is not arranged to be movable to a position (such as the third position mentioned above) beyond the first position from the second position, then it may only be possible to transfer kinetic energy in the second moving part to the closing member in a way that assists movement of the closing member towards the open position. If the closing member is stuck so that movement in either direction is prevented, then kinetic energy may be transferred from the second moving part to assist the unsticking of the closing member (by means of urging the closing member to move towards the open position) . If however only movement towards the closed position is prevented, then there may be no need to utilise kinetic energy in the second moving part. Possibly, all that may be required in such a case is for the closing member to be moved towards the open position and then reversed so as to be moved towards the closed position, so that when the closing member reaches the position at which it previously became stuck, it may have sufficient momentum to pass that position. Thus, the movement of the closing member when stuck, whether in its closed position or another position, may be assisted by means of the momentum of a part that is moving at the instant at which the valve closing member is to be moved from or past its stuck position. Such a feature is particularly advantageous, as it may allow movement of the valve to be unstuck without the need for manual maintenance of the valve . The valve may further include a cushion, for cushioning movement of one or both of the first and second moving parts . The actuator may be so arranged that when the closing member is in its open position the first moving part rests on the cushion. The actuator may be so arranged that when the closing member is in its closed position the second moving part rests on the cushion. Thus, movement of the closing member to its closed position may be cushioned as a result of the second moving part being cushioned against the cushion and movement of the closing member to its open position may be cushioned as a result of the first moving part being cushioned against the cushion. The cushion is advantageously arranged to provide a softened stop during use of the movement of a given part to a given position. The cushion may be arranged to take up play resulting from manufacturing tolerances . The valve may include a cushion, the actuator being so arranged that when the closing member is in its open position the first moving part rests on the cushion and when the closing member is in its closed position the second moving part rests on the cushion, whereby in use, upon movement of the closing member to its closed position, cushioning is provided as a result of the second moving part being cushioned against the cushion and, upon movement of the closing member to its open position, cushioning is provided as a result of the first moving part being cushioned against the cushion. It will be understood that cushioning of the movement of the closing member may be provided solely by means of a moving part, other than the closing member itself, being cushioned by the cushion. Thus, during use, the closing member itself may be caused to stop moving abruptly, but other parts of the valve may thereafter be cushioned. The cushion is preferably able in use to convert kinetic energy in the moving part that it cushions into potential energy, wherein the cushion is arranged to release that potential energy as kinetic energy in the moving part when the moving part moves away from the cushion. Thus, the cushion may assist by storing and releasing energy to assist starting the movement of a moving part from a standstill position. The cushion may for example be able in use to release kinetic energy that assists movement of the closing member from its closed position to its open position. The cushion may be able, in use, to release kinetic energy that assists movement of the closing member in the event that the closing member becomes stuck between its open and closed positions. The moving part may be the first moving part or may be the second moving part. The cushion is advantageously in the form of a spring. The term spring as used here is intended to cover any resilient means including without limitation a coiled spring, a leaf spring, or a rubber washer or other monolithic solid springy material . It is known to provide an exhaust gas recirculation valve having a soft stop at both ends of its operation by means of a separate spring at each end. Providing a single cushion in accordance with the present invention that cushions movement of both first and second moving parts is particularly advantageous however. Thus according to a second aspect of the present invention there is provided an exhaust gas recirculation valve for use with an internal combustion engine for an automotive vehicle, the valve comprising: a) a passageway, b) a closing member that is movable between a closed position in which the closing member closes the passageway and an open position which allows fluid communication through the passageway, and c) an actuator for moving the closing member between its closed and open positions, the actuator including i) a driver, ii) first and second moving parts, which together are able in use to cause movement of the closing member, and iii) a cushion, the actuator being so arranged that when the closing member is in its open position the first moving part rests on the cushion and when the closing member is in its closed position the second moving part rests on the cushion, whereby in use, upon movement of the closing member to its closed position, cushioning is provided as a result of the second moving part being cushioned against the cushion and, upon movement of the closing member to its open position, cushioning is provided as a result of the first moving part being cushioned against the cushion. It will be appreciated that features described in relation to one of the first or second aspects of the invention may be incorporated into the other. Further optional or preferred features will now be described in relation to both the first and the second aspects of the invention. Reference is made herein to a valve closing member moving between an open position and a closed position. It will be understood that the closing member may be movable to positions between said "open position" and said "closed position" and that at such positions fluid communication via the passageway may be permitted. It will also be understood that the passageway may have any suitable shape. For example, the passageway may be straight or may form part of a T-shaped valve system. The valve preferably includes a position detector arranged to detect the position of the closing member relative to its closed position, the position detector being arranged to provide a signal representative of the position of the closing member. The position detector may simply be in the form of a magnet movable relative to a suitable electronic detector. The position of the valve closing member may determine the amount of flow of gas through the passageway. The valve may for example be arranged so that at least a multiplicity of different positions of the valve closing member- may be selected according to the requirements of the proportion of exhaust gas to be recirculated. Preferably, the valve is connected to, and controllable by, a electronic control unit. The control unit may have an input that in use receives the signal from the position detector. The control unit may be arranged to detect when the valve becomes stuck and to operate the valve in such a way as to assist the unsticking of the valve. For example, the control unit may detect the sticking of the valve by comparing the movement of the closing member anticipated in response to a command to move to a certain position, or to move by a certain amount, and if the difference between the expected position, or movement, and the measured position, or movement, is greater than a predetermined threshold then the control unit will decide that the closing member is stuck. The way in which the valve is operated in order to assist the unsticking of the valve may simply comprise attempting reversal of the direction of the driver and then reversing the direction again and reattempting movement of the closing member. The control unit may be so arranged that on detection of the valve becoming stuck, the control unit causes the driver to reverse direction repeatedly. The direction may be reversed a multiplicity of times. The movement of the driver in this way may be such that movement of the second part between the first and second positions is caused. The reversals of direction of the driving of the driver may be continued at least until the control unit detects that the valve becomes unstuck. The reversals of direction of the driving of the driver may be continued at least until a predetermined number of reversals have been performed. The reversals of direction of the driving of the driver may be continued until the first of (a) the control unit detecting that the valve becomes unstuck and (b) a predetermined number of reversals having been performed. In the context of the first aspect of the invention, the direction in which the first moving part moves, when the closing member moves from its closed position to its open position, is preferably substantially opposite to the - in direction in which the second moving part moves, when it moves from its second position to its first position. When the driver is operated in a given direction, the direction in which the first moving part is caused to move is preferably opposite and substantially parallel to the direction in which the second moving part is caused to move. In the context of the second aspect of the invention, the direction in which the first moving part moves when the closing member moves from its open position to its closed position is preferably opposite to the direction in which the second moving part moves when being cushioned by the cushion as a result of the closing member moving from its open position to its closed position. The valve may be so arranged that in use the separation between the second moving part and the portion of the passageway that accommodates the closing member when in its closed position remains substantially the same whilst the closing member moves without sticking between its open and closed positions. The second moving part may be arranged for translational, for example linear, movement when the valve closing member has reached its closed position. The valve may be arranged so that in use translational movement of the second moving part relative to the valve occurs only when the valve closing member is in its closed position. The driver may be arranged to move a component of the valve between two extreme positions, the valve being closed at one extreme position and the valve being open at the other extreme position, the first and second moving parts both being caused to move by the driver as the component of the valve moves between the extreme positions, wherein the valve is arranged such that the separations of the closing member relative to the first and second moving parts respectively are not caused to change by the driver as the component of the valve moves from at least one of the two extreme positions and a position between the two extreme positions . Said position between the two extreme positions may for example be positioned relatively close to said at least one of the extreme positions . Said component may form at least a part of the second moving part. Said component may be in the form of or comprise a gear driven by the driver. The valve is preferably arranged in such a way as to allow the driver to "run on" a little after the valve has been positioned in either or both of its fully open position and its fully closed position, without causing any undesired stresses on the component of the valve. Preferably the valve is so arranged that in use when opening the valve from its closed position, the driver is able to build up some momentum before being significantly loaded, for example before causing the separation of either of the first or second moving parts relative to the portion of the passageway that accommodates the closing member when in its closed position to change. Such momentum may assist in overcoming friction caused by parts of the valve sticking. The driver may for example cause movement, for example rotational movement, of a moving part (for example the second moving part) without changing the separation of the moving part relative to the portion of the passageway that accommodates the closing member when in its closed position. Also, if the extreme position, at which the first and second moving parts are not moved by the movement of the driver, corresponds to the closed position of the valve, then when opening the valve the driver is able to build up some momentum before being significantly loaded. Such momentum may assist in overcoming friction caused by parts of the valve sticking. The driver may be in the form of a prime mover. The driver may be in the form of a motor, for example an electric motor. The driver need not be connected directly to the first or second moving parts. The movement of the first and second moving parts caused by the driver may be direct or indirect. Drive may be transmitted to the first moving part and/or the second moving part via one or more gears . The second moving part advantageously includes means for converting rotational motion from the driver into linear motion of the first moving part . The second moving part may for example include a portion that engages with a corresponding portion on the first moving part. One moving part may for example comprise a generally helical groove which accommodates a pin connected to the other moving part. In such a case the parts might be arranged such that rotation of the pin about the axis of the helical groove is prevented such that rotation of the groove relative to the pin causes the pin to follow the groove and thereby cause the first and second moving parts to move relative to each other along the axis of the helical groove. The groove may be in the form of an aperture (for example a groove with side walls, but no base) or a recess (for example a groove having a base from which side walls extend) . In a similar manner, one of the first and second moving parts may comprise a screw thread that engages with a portion, for example another screw thread, on the other part. If one part is prevented from rotating with the other part, rotation of the parts relative to each other will cause motion of the two parts relative to each other along the axis of the screw thread. The second moving part may be arranged to be movable relative to the driver in a direction substantially parallel to the direction of the linear motion of the first moving part. The movement of the second moving part is preferably constrained such that linear movement in a direction transverse to the motion of the first moving part is substantially restricted. The movement of the second moving part may be constrained such that there is resistance to movement in a direction parallel to the motion of the first moving part. The constraining of movement may for example be achieved by means of the second moving part being accommodated between two bearings, at least one of which being deformable or translationally moveable. One or more of the bearings may be in the form of a cushion as described above. One or more of the bearings may be positioned between the second moving part and such a cushion. Thus, whilst the movement is constrained and restricted during movement of the first moving part, the arrangement of the second moving part is advantageously such that it is not entirely prevented from moving in such a way that changes its separation from the portion of the passageway that accommodates the closing member when in its closed position. For example, the second moving part is advantageously arranged to move, so as to change its separation from that portion of the passageway, when the first moving part reaches one end of its possible movement during normal operation. The first moving part may comprise a rod. The closing member may comprise a poppet. The poppet may be fixed at the end of the rod of the first moving part. The valve closing member preferably has sufficient play in its movement to allow correct alignment relative to the passageway to ensure a tight seal over the passageway when the closing member is in its closed position. For example, in the case where the valve closing member comprises a poppet fixed on the end of a rod, there may be some play in the position of the rod relative to the rest of the valve and/or the fixing of the poppet on the end of the rod may be flexible, thereby permitting some relative movement between the poppet and the rod. Reference is made herein to an exhaust gas recirculation valve. However, it will be appreciated that the present invention may have application in relation to any type of valve, and in particular in relation to valves where sticking of the valve is a potential problem. Thus the present invention also provides a valve having the features of the first and/or second aspects of the invention, but being a valve suitable for any application including without limitation application as an exhaust gas recirculation valve. The present invention also further provides an internal combustion engine for an automotive vehicle including an exhaust outlet and a combustion fluid inlet, the exhaust outlet being connected via a passageway of an exhaust gas recirculation valve to the combustion fluid inlet, wherein the exhaust gas recirculation valve is a valve according to the present invention as described herein. The engine may further include a control unit arranged to perform the function of the control unit described above in relation to the exhaust gas recirculation valve of the present invention. The control unit of the engine may perform other functions, such as engine management functions. In relation to this aspect of the invention there is also provided a valve having a passageway closable by a closing member and an associated control circuit, the movement of the closing member being controllable by the control unit, the valve including a position detector arranged to detect the position of the closing member, the position detector being arranged to provide a signal representative of the position of the closing member to the control unit, wherein the control unit is arranged to detect when the valve closing member becomes stuck at any position between its fully closed position and its fully open position and to operate the valve in such a way as to assist the unsticking of the valve closing member. Features described herein relating to the valve of the present invention may of course be incorporated into the valve according to this aspect of the invention. The present invention also provides a method of controlling the recirculation of exhaust gas in an internal combustion engine of an automotive vehicle, the method including providing an internal combustion engine including an exhaust outlet and a combustion fluid inlet, providing a valve between the exhaust outlet and the combustion fluid inlet, the valve including a first moving part for shutting and opening the valve, and controlling the flow of recirculation of exhaust gas into the engine by means of operating the valve by moving the first moving part. According to a first aspect of the method of the invention the valve includes a second moving part and a driver for moving both the first moving part and the second moving part and the method includes a step of opening the valve by means of the driver moving the second moving part first, whilst the first moving part is substantially stationary and the valve is closed, transferring momentum from the second moving part to the first moving part, the first moving part then being driven by the driver to cause the valve to open, preferably whilst the position of the second moving part relative to the valve in the general direction of movement of the first moving part remains substantially the same. According to a second aspect of the method of the invention the valve includes a second moving part, a driver for moving both the first moving part and the second moving part, and a cushion, the method including the following steps: fully opening the valve, the movement of the valve being cushioned by means of the first moving part being cushioned by the cushion, and fully closing the valve, the movement of the valve being cushioned by means of the second moving part being cushioned by the cushion. According to this aspect of the method the kinetic energy absorbed by the cushion is advantageously released to aid subsequent movement of the moving part previously cushioned by the cushion. Features of the apparatus of the present invention may be incorporated into the method of the invention and vice versa. By way of example, embodiments of the present invention will now be described with reference to the accompanying drawings of which: Figure 1 shows a perspective view of a valve according to a first embodiment of the invention; Figure 2 shows an exploded perspective view of the lower half of the valve as shown in Figure 1; Figure 3 shows a cross-section of the valve as shown in Figure 1; Figure 4a shows a schematic cross-sectional view of the valve when in a position midway between being open and closed together with a schematic diagram illustrating the position of parts of the valve in that position; Figure 4b is the same as Figure 4a, except that the valve is fully open; Figure 4c is the same as Figure 4a, except that the valve is in a position in which the valve is just closed; Figures 4d and 4e are the same as Figure 4a, except that the Figures show the valve in respective positions beyond the closed position shown in Figure 4c; and Figure 5 is a cross-sectional view of a second embodiment of the invention .

Figure 1 shows the general external shape of a valve 2 comprising a valve body 4 that defines a passageway 6 through which in use exhaust gas may flow and a generally funnel shaped valve seat 8 (the seat 8 being hidden from view in Figure 1) in the passageway 6. The valve is designed for use as an exhaust gas recirculation valve for use in an engine of a diesel car. When the valve 2 is open, exhaust gas is allowed to pass through the passageway 6 from the engine exhaust back to the combustion chamber. Recirculating such exhaust gases can allow harmful emissions to be reduced. There may however be circumstances in which it is not appropriate to recirculate exhaust gases, in which cases the valve 2 may be closed. The opening and closing of the valve when in situ is managed by a control unit (not shown in Figure 1). Figures 2 and 3 show the various component parts of the valve 2, Figure 2 showing various parts of the valve in an exploded perspective view and Figure 3 showing a cross-section of the valve (when the valve is just closed) taken across a plane containing the axis of the valve seat 8. The parts of the valve will now be described with reference to Figures 2 and 3. A poppet 10 mounted on a rod 12 is movable between an open position, in which gas can flow through the passageway 6 (so that the valve 2 is in an open state) and a closed position in which the poppet 10 sits on and seals over the valve seat 8 and therefore seals the passageway 6 so that exhaust gases are prevented from passing through the passageway 6 (so that the valve 2 is in a closed state) . The poppet 10 is rigidly mounted on the rod 12, but there is sufficient play in the movement to allow the poppet 10 to align correctly on the valve seat 8. The rod 12 and poppet 10 are mounted for translational movement in a direction along the longitudinal axis of the rod 12 to facilitate opening and closing of the valve 2. The end of the rod 12 opposite the poppet 10 is held by a boss 14. A pin 16 perpendicular to the axis of the rod 12 is rigidly fixed to and passes through the centre of the boss 14, so that the ends 18 of the pin 16 project from either side of the boss 14. Each end 18 of the pin 16 is accommodated by a linear guide 20 that guides translational movement of the pin 16, and therefore also of the boss 14 and rod 12, in a direction parallel to the axis of the rod 12. The guides 20 also restrict (and substantially prevent) rotational movement of the boss 14 and therefore the rod 12. The boss 14 is housed within a short tube 22, in which two helical grooves 24 are defined. The tube 22 has a cross-sectional shape generally in the form of a ring. The tube 22 is positioned between the linear guides 20 and is mounted for rotational movement. The pin 16 passes through each helical groove 24, the groove 24 having a width that is sized to correspond to the diameter of the pin 16. The valve 2 also includes an electric motor 26 for driving rotation of the tube 22. The driving of the tube 22 causes the poppet 10 to open and close the valve as will be described in further detail below. The shaft of the motor 26 is connected to a pinion gear 28 which drives a hemi-annular ring gear 30, which is rigidly fixed to the tube 22. The tube 22 is positioned so that when the poppet 10 is midway between its open and closed positions the end 22a of the tube 22 furthest from the poppet 10 rests against a thrust washer 32 and the end 22b nearest the poppet 10 rests against a spring washer 31, which itself bears against an annular compression spring 34. The rod 12 freely passes through the centre of both the spring washer 31 and the annular compression spring 34. The spring washer 31 extends inwardly enough that when the valve 2 is in its fully open position, the end 14a (not referenced in Figures 2 or 3) of the boss 14 nearest the poppet 10 rests against the spring washer 31, which bears against the spring 34. The rod 12 also passes through an annular seal member 36 that is secured by a push- fit in a recess 38 formed by the valve body 4 at a position between the spring 34 and the poppet 10. A further compression spring 40 is provided which is accommodated in an annular recess 42 defined in the valve body 4, the recess 42 facing the hemi-annular ring gear. This further spring 40 acts as a return spring, returning the poppet 10 to a failsafe position (as is standard practice in relation to such valves) in the event of certain parts of the valve 2 failing. It will be seen that as the motor 26 is driven, the tube 22 is rotated by means of the gears 28, 30, and the pin 16 is urged by the grooves 24 either up or down depending on the direction of motion. The valve includes a position detector comprising a magnet 44 mounted on the end of the rod 12 opposite the end on which the poppet 10 is mounted. An integrated circuit 46 able to ascertain the position of the magnet in the direction of the longitudinal axis of the rod 12 is positioned, opposite to and facing the magnet 44, on a printed circuit board (PCB) 48. A control unit 50 for controlling operation of the valve is connected via signal carrier 52 to pins 54 linked to the PCB 48. The travel of the rod between its extreme positions is about 6mm. The integrated circuit 46 is able to detect with reasonable accuracy the linear position of the rod to within the nearest 0.05mm. Operation of the valve will now be described with reference to Figures 4a to 4e. Figures 4a to 4e show schematically the valve in various positions. Figure 4a shows the valve 2 in a position midway between being fully open and closed as the valve is moving to its fully open position. Figure 4a shows the valve seat 8, the poppet 10, the rod 12, the boss 14, the tube 22, the thrust washer 32, and the spring 34. Figure 4a also shows separately a schematic representation of the position of one end 18 of the pin 16 in the helical groove 24 (which has been transformed into a flat representation of the groove for ease of understanding and of comparison between the respective Figures) . Other parts of the valve are not shown for the sake of clarity and the dimensions of the various parts and the amounts by which they move have been exaggerated to ease understanding of the operation of the valve . The helical groove 24 has one end (the lower end as shown in Figures 4a to 4e) in which the pin 16 is positioned when the valve is in its open position and another opposite end (the upper end as shown in Figures 4a to 4e) in which the pin is positioned when the valve is in its closed position. The groove 24 has a gradient that is constant between the open position and to a position beyond the position at which the valve is just closed. The gradient then flattens beyond this position to the end of the groove 24. In Figure 4a one end of the tube 22 rests on the spring washer 31 which itself bears against the spring 34 (in its uncompressed state) , and the other end bears against the thrust washer 32. As the tube 22 is rotated anti-clockwise (when viewed from the side opposite the poppet - i.e. from above as shown in the Figures) , the tube 22 bears against the thrust washer 32 and the boss 14 is caused to move away from the valve seat 8, thereby also moving the poppet 10 away from the valve seat 8. The ends 18 of the pin 16 are position roughly midway along the helical grooves 24. As the poppet 10 approaches its fully open position, the end 14a of the boss 14 nearest the poppet contacts the spring washer 31 which itself bears against the spring 34 and starts to compress the spring 34. When the poppet 10 reaches its fully open position as shown in Figure 4b, the spring 34 is significantly compressed by the boss 14 and the tube 22 bears against the thrust washer 32 but is no longer in contact with the spring, via the spring washer 31. The poppet 10, when moved to its fully open position, is therefore cushioned by the spring 34 before reaching its fully open position, thereby providing a soft stop (as the electric motor 26 works against the resilient loading of the spring 34) . The pin 16 is at the end (the lower end as shown in Figure 4b) of the helical groove 24. When the valve is moved from the fully open position as shown in Figure 4b to its just closed position, the parts move from their positions as shown in Figure 4b, via their positions as shown in Figure 4a, to the positions as shown in Figure 4c. Initially, the spring 34 assists the movement as it releases the stored potential energy as kinetic energy as it expands. As the tube 22 is rotated clockwise, the tube 22 bears against the spring 34 (via the spring bearing 31) very slightly compressing the spring 34 and the boss 14 is caused to move towards the valve seat 8 thereby also moving the poppet 10 towards the valve seat. At the moment at which the poppet contacts the valve seat 8 (the position shown in Figure 4c) , the pin 16 is at a position near the end (the upper end as shown in Figure 4b) of the helical groove 24. As the motor 26 continues to turn and the tube 22 is rotated further clockwise, the poppet and rod are prevented from moving by virtue of the poppet 10 bearing against the valve seat 8. As a result of the rotational movement of the tube 22, the pin 16 still follows the groove 24 in the tube 22 and because the rod 12 and therefore the pin 16 are prevented from moving away from the valve seat 8, the tube 22 moves towards the valve seat 8 and away from the thrust bearing 32. The end 22b of the tube 22 nearest the poppet 10 therefore bears against the spring washer 31 and compresses the spring 34. As the motor 26 has to work against the spring 34, the spring aids the stopping of the motor. The same spring 34 therefore provides a soft or cushioned stop of the motor at both ends of its movement. Figure 4d shows the poppet 10 in its fully closed position, the pin 16 having moved further towards the end of the groove 24 to a point just before the gradient of the groove flattens out. The pin 16 is therefore as close to the end (the upper end as shown in Figure 4d) of the tube 22 as it is permitted to reach. The spring 34 is at this point significantly compressed. The motor 26 is able to continue turning and turn the tube 22 even further clockwise beyond the position shown in Figure 4d. Again the poppet 10 and rod 12 are prevented from moving (upwards in Figure 4e) by virtue of the poppet 10 bearing against the valve seat 8. The spring 34 is compressed by the tube 22, which effectively resiliently urges the poppet against the valve seat. Since the gradient of the helical groove 24 in the region of the pin 16 between the positions shown in Figure 4d and 4e is zero, the tube 22 rotates and the pin 16 remains in the same position. The motor 26 is therefore able to overshoot both the position at which the poppet 10 initially closes over the valve seat 8 and also the position at which the spring 34 is "fully" compressed. In Figure 4e, the pin is shown to have moved to the very end of the flat (zero gradient) part of the groove 24. When the valve is to be opened (from the fully closed position as shown in Figure 4e) , the motor 26 starts to rotate the tube 22 anti-clockwise, which initially effects no translational movement of the tube. The pin 16 however travels along the flat part of the groove 24 and the motor and associated gears build up momentum. The parts of the valve 2 then reach the position shown in Figure 4d. The pin 16 then starts to move along the sloped part of the helical groove 24 and motion of the tube 22 away from the valve seat 8 is caused. Initial movement of the tube 22 is helped by the rotational momentum carried in the motor 26, and the gears 28, 30. Also, the potential energy stored in the spring 34 is released and the spring 34 assists movement of the tube. When the tube 22 hits the thrust bearing 32 (shown in Figure 4c) , the boss 14 and therefore the rod 12 and poppet 10 are quickly forced downwards . The momentum in the various parts of the valve that are moving, before the rod 12 and poppet 10 start moving, helps overcome the friction that might otherwise prevent movement of the poppet 10 from the valve seat 8. The poppet 10 then moves via the intermediate position shown in Figure 4a to the fully open position as shown in Figure 4b as described above. During normal operation, the movement of the poppet 10 is controlled and monitored by the control unit 50. The control unit 50 assesses various parameters and as a result determines the amount of recirculation of exhaust gases that is required. The control unit 50 calculates the position of the poppet required to provide the desired amount of recirculation and then causes the motor 26 to move the tube 22 to move the boss 14 to the appropriate position. The control unit monitors that the desired position has been achieved by means of feedback from the integrated circuit 46 that detects the position of the magnet 44 and therefore the position of the rod 12 and poppet 10. If the movement of the magnet 44 expected by the control unit 50 is not matched by the measurement received by the control unit 50 from the integrated circuit 46, then the control unit assumes that the poppet 10 has got stuck. If the valve 2 is allowed to cool, for example if the engine is stopped for long enough to allow the engine to cool to ambient temperature, the sticky deposits in the region of the valve seat 8, poppet 10 and rod 12 may become more viscous, possibly solidifying, thereby causing the valve to become stuck in an open position. If the control unit 50 detects that the poppet 10 is stuck, for example in a position mid-way between the fully open position and the fully closed position (the position shown in Figure 4a for example) it takes action to dislodge the poppet 10 from its stuck position. First, the control unit 50 causes the tube 22 to be rotated clockwise. The poppet 10 and rod 12, if still stuck, are prevented from moving and, as a result of the pin 16 following the groove 24 in the tube 22, the tube 22 moves towards the valve seat 8 and away from the thrust bearing 32 (in much the same way as it moves when the valve is fully closed) . The tube 22 therefore bears against the spring washer 31 and compresses the spring 34. Then the motor 26 turns the tube 22 anti-clockwise, causing the pin 16 to move along the helical groove 24 and thereby causing motion of the tube 22 away from the valve seat 8. The potential energy stored in the spring 34 is released and the spring 34 assists movement of the tube so that when the tube 22 hits the thrust bearing 32, momentum is rapidly transferred to the boss 14, the rod 12 and the poppet 10. If as a result of such a "hammer action" the poppet is caused to move, then the control unit 50 resumes normal operation. If the control unit 50 detects that the poppet 10 is still stuck in position, the process is repeated. If the control unit detects that the poppet 10 is stuck such that movement in only one direction is prevented the control unit 50 turns the motor in the opposite direction and then reverses direction so as to "run-up" to the sticking point. Such reciprocating movement is continued until the poppet is moved beyond the sticking position or until a predetermined number of unsuccessful attempts have been made at moving the poppet 10. In the event that the control unit 50 is unable to move the poppet 10 from or beyond its stuck position, the control unit 50 may send an output signal warning the user of the engine (for example the driver of the car) that there is a fault and immediate maintenance is required. The valve has several important features . Firstly, a single spring provides a soft stop at both ends of movement of the valve. That same spring also assists movement of the poppet when opening the valve. Before the parts of the valve move to open the poppet when in its closed position, the parts move to gain momentum to assist in breaking the seal that might be made owing to the tar-like residue in the region of the valve seat and the poppet. The motor is able to run on significantly when closing the valve. Also the valve may be able to utilise the spring to assist movement in the event that the poppet becomes stuck between the open and closed positions . Figure 5 shows a cross-sectional view of a valve 102 according to a second embodiment of the invention. The second embodiment operates in much the same way as the first embodiment and as such only those features that differ will now be described. Instead of a helically grooved tube, there is provided a screw-threaded tube 122 which engages with a screw thread formed on the boss 114. The tube 122 is rotated by the motor 126 and the boss 114 is prevented from rotating by means of a side protrusion (not shown in Figure 5) on the end of the boss 114 furthest from the poppet 110 (the upper end as shown in Figure 5) which is guided in a single slot, or linear guide (also not shown in Figure 5) . Thus rotation of the motor 126 causes the boss 114 and therefore the poppet 110 to move linearly towards (or away from) the valve seat 108. Because the screw thread has a constant pitch there is no zero gradient screw thread allowing the motor to run on beyond the fully closed position without causing movement of the tube 122. It will be appreciated that various modifications may be made to the above-described embodiment of the invention. By way of example, some such modifications will now be described. The gradient of the helical groove could be varied along its length so as to control the gearing of the movement of the poppet relative to the movement of the pinion gear of the motor. The helical groove could have a section of zero gradient at both ends, thereby enabling the motor to "run on" more both when closing and opening the valve . The thrust bearing could be in the form of a spring. In that way, the hammer action provided by the rapid transfer of energy from the tube to the boss might be softened, but it would be possible to turn the tube in either direction in the event that the poppet becomes stuck. Also, such an arrangement would assist movement of the poppet from the fully open position, as the spring replacing the thrust bearing could transfer kinetic energy to the boss, because the tube would start rotating and moving linearly before causing movement of boss.

Claims

1. An exhaust gas recirculation valve for use with an internal combustion engine for an automotive vehicle, the valve comprising a) a passageway, b) a closing member that is movable between a closed position in which the closing member closes the passageway and an open position which allows fluid communication through the passageway, and c) an actuator for moving the closing member between its closed and open positions, the actuator including i) a first moving part that in use causes movement of the closing member, ii) a second moving part, and iii) a driver that in use causes movement of the first and second moving parts, wherein the actuator is so arranged that in use: at the instant at which the closing member reaches the closed position from the open position as a result of the driver being operated to move the first moving part, the second moving part is at a first position, and thereafter on continued operation of the driver the second moving part moves from the first position to a second position, and when the second moving part is in the second position, the closing member is in the closed position, and the driver is operated to open the valve, the second moving part moves from its second position to its first position, at which position it has kinetic energy that assists movement of the closing member from its closed position to its open position.

2. A valve according to claim 1, wherein the actuator is so arranged that in use in the event that the closing member becomes stuck during movement between its closed position and its open position, continued operation of the driver in a direction that would normally move the closing member towards its closed position causes the second moving part to move from its first position to its second position.

3. A valve according to claim 1 or claim 2, wherein the valve is so arranged that in the event that the closing member becomes stuck during movement between its closed position and its open position, the second moving part may be moved by the driver from its first position to another position and then moved back to its first position, so that when moved back to its first position it has kinetic energy that assists movement of the closing member from its stuck position.

4. A valve according to any preceding claim, wherein the valve further includes a cushion, the actuator being so arranged that when the closing member is in its open position the first moving part rests on the cushion and when the closing member is in its closed position the second moving part rests on the cushion, whereby in use movement of the closing member to its closed position is cushioned as a result of the second moving part being cushioned against the cushion and movement of the closing member to its open position is cushioned as a result of the first moving part being cushioned against the cushion.

5. A valve according to claim 4, wherein the cushion is able in use to convert kinetic energy in the moving part that it cushions into potential energy, and wherein the cushion is arranged to release that potential energy as kinetic energy in the moving part when the moving part moves away from the cushion.

6. A valve according to claim 4 or claim 5, wherein the cushion is able in use to release kinetic energy that assists movement of the closing member from its closed position to its open position.

7. A valve according to any of claims 4 to 6, wherein the cushion comprises a spring.

8. A valve according to any preceding claim including a position detector arranged to detect the position of the closing member relative to its closed position, the position detector being arranged to provide a signal representative of the position of the closing member.

9. A valve according to any preceding claim, wherein the valve is connected to and controllable by a electronic control unit.

10. A valve according to claim 9, wherein the control unit has an input that in use receives the signal from the position detector and the control unit is arranged to detect when the valve becomes stuck and to operate the valve in such a way as to assist the unsticking of the valve.

11. A valve according to claim 10, wherein the control unit is so arranged that on detection of the valve becoming stuck, the control unit causes the driver to reverse direction repeatedly.

12. A valve according to any preceding claim, wherein the direction in which the first moving part moves, when the closing member moves from its closed position to its open position, is substantially opposite to the direction in which the second moving part moves, when it moves from its second position to its first position.

13. A valve according to any preceding claim, wherein the valve is so arranged that in use the separation between the second moving part and the portion of the passageway that accommodates the closing member when in its closed position remains substantially the same whilst the closing member moves without sticking between its open and closed positions.

14. A valve according to any preceding claim, wherein the driver is arranged to move a component of the valve between two extreme positions, the valve being closed at one extreme position and the valve being open at the other extreme position, the first and second moving parts both being caused to move by the driver as the component of the valve moves between the extreme positions, wherein the valve is arranged such that the separations of the closing member relative to the first and second moving parts respectively are not caused to change by the driver as the component of the valve moves from at least one of the two extreme positions and a position between the two extreme positions .

15. A valve according to any preceding claim, wherein the second moving part includes means for converting rotational motion from the driver into linear motion of the first moving part.

16. A valve according to claim 15, wherein the second moving part is movable relative to the driver in a direction substantially parallel to the direction of the linear motion of the first moving part.

17. A valve according to claim 15 or claim 16, wherein the movement of the second moving part is constrained such that linear movement in a direction transverse to the linear motion of the first moving part is substantially restricted.

18. A valve according to any preceding claim, wherein the first moving part comprises a rod and the closing member comprises a poppet, fixed at the end of the rod.

19. A valve according to any preceding claim, wherein the valve closing member has sufficient play in its movement to allow correct alignment relative to the passageway to ensure a tight seal over the passageway when the closing member is in its closed position.

20. An exhaust gas recirculation valve for use with an internal combustion engine for an automotive vehicle, the valve comprising: a) a passageway, b) a closing member that is movable between a closed position in which the closing member closes the passageway and an open position which allows fluid communication through the passageway, and c) an actuator for moving the closing member between its closed and open positions, the actuator including i) a driver, ii) first and second moving parts, which together are able in use to cause movement of the closing member, and iii) a cushion, the actuator being so arranged that when the closing member is in its open position the first moving part rests on the cushion and when the closing member is in its closed position the second moving part rests on the cushion, whereby in use, upon movement of the closing member to its closed position, cushioning is provided as a result of the second moving part being cushioned against the cushion and, upon movement of the closing member to its open position, cushioning is provided as a result of the first moving part being cushioned against the cushion.

21. An internal combustion engine for an automotive vehicle including an exhaust outlet and a combustion fluid inlet, the exhaust outlet being connected via a passageway of an exhaust gas recirculation valve to the combustion fluid inlet, wherein the exhaust gas recirculation valve is a valve according to any of the preceding claims .

22. An engine according to claim 21, the engine further including a control unit arranged in accordance with the control unit of the valve according to any of claims 9 to 11.