BUTTERFLY VALVE ACTUATOR

Abstract: An actuator for mechanical or electrical actuation of a butterfly valve is able to move between fixed positions, and to move a butterfly between fixed end stops whilst accommodating tolerances. The actuator includes a compressible link (18, 21, 27) and levers (15, 19, 23) arranged to give positive travel insensitive movement of the butterfly (14).

Description: BUTTERFLY VALVE ACTUATOR This invention relates to an actuator for a butterfly valve, and particularly to an actuator for an exhaust brake of the kind comprising a butterfly valve pivotable in an exhaust duct of a vehicle. Exhaust brakes of the butterfly valve type are usually provided in the exhaust pipe, and can be closed to obstruct the exhaust tract, thereby placing a back pressure on the vehicle engine which tends to retard the vehicle. Such an arrangement works well where a source of air under pressure is available for actuation, as is provided on a typical heavy goods vehicle. An air actuator is not travel sensitive, and thus the travel limits of the butterfly valve are determined by fixed stops of the butterfly. In other words the actuator piston travels under air pressure until the butterfly reaches an end stop; the distance moved by the piston is not important so long as the range of movement is sufficient for the butterfly. Such an arrangement has the advantage of being able to compensate for wear, and can accommodate a range of tolerances when the apparatus is first assembled, and without requiring a special adjustment procedure. Some vehicles do not have a source of air under pressure. Accordingly an electrical or mechanical actuator is required. Such mechanisms are travel sensitive in that they generally require movement from one end stop to another. For example a mechanical linkage, like a gear shift lever, requires movement from one fixed position to another, and a detent to hold the linkage in one or other position. An electrical actuator, for example a motor, requires a switch for deactivation at the desired travel setting. Clearly the travel stops required for mechanical and electrical actuators must be carefully determined so as not to prevent the butterfly reaching either of its end positions. If these stops are not accurately set there will be a reduction in exhaust brake efficiency or internal stress in the actuator mechanism. The settings may require frequent checking in order to compensate for wear. It might be possible to include a force sensitive switch to deactivate an electric motor at a butterfly end stop, but such an arrangement is somewhat complex and expensive. In any event such a solution is not appropriate for a mechanical linkage since the operator will have no indication that an end stop has been reached apart from increasing resistance to movement; the possibility of over stressing the operating linkage cannot be excluded. An integral safety device may be included to prevent pressure upstream of a closed butterfly valve exceeding a pre-determined limit. One kind of prior safety device closes the butterfly valve through a spring and incorporates a butterfly having its spindle axis offset from a diameter of the exhaust duct. The offset butterfly will exert a turning moment which increases as upstream pressure increases; this moment can be arranged to react through the spring and, by suitable choice of lever ratio and spring load, the butterfly can be arranged to open to release excess upstream pressure. It would be useful for a solution to the problem of mechanical and electrical actuation to also incorporate an integral safety device of the aforementioned kind. According to the invention there is provided a butterfly valve having an annular casing and a butterfly spindle protruding through the wall thereof, and an actuating mechanism comprising: a) a first lever connected to said spindle for pivoting the butterfly about the spindle axis between end stops; b) a frame attached to said casing; c) a resiliently compressible link pivotally mounted at one end to said frame about a first axis, and pivotally mounted at the other end to said first lever about a second axis; d) a second lever pivotally mounted at one end to said frame about said first axis; and e) a third lever pivotally mounted at one end to the other end of said second lever about a third axis, and pivotally mounted at the other end about said second axis, the third lever having a slotted connection at said second axis to permit a variation in effective length of said third lever; and the mechanism being arranged such that f) the second axis is movable in an arc through a straight line connecting the spindle axis and said first axis by compression of said link, said first lever thereby pivoting said butterfly between said end stops; g) in the closed position of said valve, the length of said link is less than the combined distance between the first and third axes and between the third and second axes; h) in the open condition of said valve the length of said compressible link is determined by said combined distance; i) the position of one end of said slot determines the maximum extension of said compressible link, and the position of the other end is sufficient to permit free movement of said linkage between end stops of said butterfly; and j) an actuating link is adapted to be pivotally connected to said mechanism at said third axis. In a preferred embodiment the casing is of circular cross section and the spindle axis is offset from a diameter of the casing, the resultant moment on the butterfly caused by gas pressure in the casing being reacted by the compressible link. The compressible link may be a coiled compression spring. Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying schematic drawings in whi ch : - Fig. 1 is an elevation showing the mechanism of the invention in one end position; Fig. 2 corresponds to Fig. 1 and shows a mid-position; Fig. 3 corresponds to Fig. 1 and shows the other end posit ion ; Fig. 4 is an axial cross section through part of the mechanism; and Fig. 5 is a graph illustrating the force/travel characteristic of the linkage. With reference to Figs. 1-4 of the accompanying drawings, a tubular housing 11 has an inner wall 12 and end flanges 13 for connection to pipe sections of a vehicle exhaust system. A butterfly 14 is pivoted on a spindle 1 a close to a diameter of the housing 11, and on one side the butterfly spindle protrudes through the housing for connection to a lever 15. Arcuate movement of the lever 15 moves the butterfly 14 from the closed to the open condition, as illustrated in Figs. 1 and 3. End stops are constituted by abutment of the butterfly with the housing 11 (Fig. 1). A generally oblong flat mounting plate 16 is secured to the housing 11 in any convenient manner, and has mounted thereon a linkage and spring assembly best illustrated in Fig. 4. The plate has an upstanding pivot pin 17 defining an axis 17a on which are independentl journalled a female spring support 18 and one end of a plain arm 19. A male spring support 21 fits within the female spring support 18, as illustrated, and has a pivot pin 22 protruding therefrom at the top and bottom and defining an axis 22a. A slotted arm 23 is pivotally connected to pivot pin 22 at a slot 24 and via another pivot pin 25 about an axis 25a to the other end of plain arm 19. The male and female spring supports have spring seats 26 between which a coiled spring 27 is fitted under compression. The male and female spring supports fit together in order to permit relative movement only along the axis of the spring 27. As will be apparent from Fig. 4, the spring 27 urges apart the spring supports 18,21 to the extent permitted by the plain and slotted arms 19,23; the pivot pin 22 being at the right hand end of slot 24 as illustrated. The lever 15 is pivotally connected to pivot pin 22. An actuating link 28 movable under vehicle driver control is connected to pivot pin 25. The pivot pins 17,22,25 may be secured in any suitable manner and may for example be force fitted in one component whilst permitting the other parts to pivot relative thereto. The parts may be retained on the pivot pins in any suitable manner, for example by circlips, and low friction washers may be inserted between adjacent parts if desired. The levers and arms may be arranged differently around the spring supports 18,21 if desired; for example the arms 19,23 could be located between the spring supports and the mounting plate, or could be cranked. Operation of the device is as follows. Fig. 1 illustrates the exhaust brake in use with the butterfly 14 closed. The spring 27 is fully extended, and the pivot pin 22 is loosely guided in the slot 24, as viewed. Sufficient slack is provided in the combined length of arms 19,23 to ensure that the butterfly closes tightly against the inner wall 12 under the action of spring 27 and lever 15. This is achieved by ensuring that the combined length is slightly longer than the separation of the spring supports 18,21, so that the arms 19,23 are at a slight angle to one another. As will be readily appreciated, in this condition there is no strain on the operating link 28, and the arms 19,23 are somewhat loose due to the slot 24. Since the butterfly spindle is offset, increasing gas pressure will exert a turning moment on the butterfly against the effect of the spring. The slot 24 permits movement of the lever 15 and male spring seat 21 without placing any load on the operating link 28. Reactive movement of the butterfly to release excess gas pressure is generally less than 10°, and the slot is dimensioned to permit sufficient free play. When it is desired to open the butterfly, the driver moves the operating link 28 in the direction of arrow A (Fig. 2). The clearance is taken up and the pivot pin 22 is contacted by the right hand end of slot 24. The spring 27 is compressed as the arms 19,23 pull the spring supports together and thus provide the necessary resistance to movement of link 28. The lever ratio on the butterfly is initially high, and this substantial mechanical advantage helps to overcome the load of spring 27. Fig. 2 illustrates the 'balanced' condition with the spring 27 at minimum length. Slight further movement of the link 28 causes the linkage to snap clockwise towards the position illustrated in Fig. 3 in which the spring is at the maximum extension permitted by arms 19 and 23. The lever 15 consequently places the butterfly in the fully open condit ion. In moving from the balanced condition of Fig. 2 to the fully extended condition of Fig. 3 it is important that no load is placed on the operating link 28, for otherwise maladjustment of the link might prevent free movement of the lever 15. The slot 24 permits free movement of pivot pin 22 leftwards as the lever moves ant i -clockwi se from the inline condition illustrated in Fig. 2. As the lever 15 turns further ant -clockw se the pin 22 returns to the right hand end of slot 24 where it carries arm 23 clockwise about pivot pin 25 until it is in line with arm 19. At this point the spring is at the maximum permitted extension, as shown in Fig. 3, with arms 19 and 23 in tension. Note that in moving from the condition of Fig. 2 to the condition of Fig. 3 the angle of arm 19 does not change significantly with respect to the axis of housing 11, and accordingly no load is placed on the operating link 28. In practice, due to friction effects, it is necessary to arrange for the link to pull the spring supports 21 slightly past the 'balanced' position of Fig. 2. Provided the link 28 has sufficient travel to pull the mechanism through this position, the actual end positions of the link are not critical since in both cases only the load of the spring is effective. Fig. 5 illustrates the travel/force characteristics of the invention. The dotted line shows the variation in operating load (L) from the 'balanced' condition (Fig. 2), which is coincident with the Y axis, in the direction of one or other end position (Figs. 1 and 3). The operating load in the other direction will be substantially a mirror image on the other side of the Y axis, and the operating load in the balanced condition will approach zero. The solid line shows the force exerted by spring 27, and is thus representative of the torque (T) acting on the butterfly from the balanced condition to one end stop. The torque in the other direction is again substantially a mirror image. A typical stop position for the butterfly is represented by line A, though this could be shifted along the X axis according to precise design requ rements. As the graph indicates, torque is high at the end stop whereas operating load is relatively low. More importantly the operating load is relatively constant despite a very significant change in the torque at the butterfly. This characteristic is a result of the initial lever advantage, and gives good 'feel' to an operator of a mechanical linkage. Sudden and uncontrolled movement of the butterfly in the manner of electrical switch contacts throwing from one end position of a switch to the other is avoided. This latter characteristic would be the effect of a direct linkage, and would be travel sensitive as previously ment ioned. The relatively constant operating load is also much more suitable for servo actuation, by e.g. an electric motor. Furthermore, for the reasons given above, the travel stops of e.g. an electric motor need not coincide with the travel stops of the butterfly, nor do such stops require adjustment in service. Although the invention has been described in relation to an exhaust brake, it is equally suitable for any butterfly valve which must be moved between end stops in a manner which does not give an interaction between the operating stroke of the actuator and the travel of the butterfly.

Claims: CLAIMS : 1. A butterfly valve having an annular casing (11) and a butterfly spindle (14a) protruding through the wall thereof, and an actuating mechanism comprising: a) a first lever (15) connected to said spindle (14a) for pivoting a butterfly (14) about the spindle axis between end stops; b) a frame (16) attached to said casing (11); c) a resiliently compressible link (18,21,27) pivotally mounted at one end to said frame (16) about a first axis (17a), and pivotally mounted at the other end to said first lever (15) about a second axis (22a); d) a second lever (19) pivotally mounted at one end to said frame (16) about said first axis (17a); and e) a third lever (23) pivotally mounted at one end to the other end of said second lever (19) about a third axis (25a), and pivotally mounted at the other end about said second axis (22a), the third lever (23) having a slotted connection (24) at said second axis (22a) to permit a variation in effective length of said third lever (23); and the mechanism being arranged such that f) the second axis (22a) is movable in an arc through a straight line connecting the axis of the spindle (14a) and said first axis (17a) by compression of said link (18,21,27), said first lever (15) thereby pivoting said butterfly (14) between said end stops; g) in the closed position of said valve, the length of said link (18,21,27) is less than the combined distance between the first and third axes (17a, 25a) and between the third and second axes (25a, 22a); h) in the open condition of said butterfly the length of said compressible link (18,21,27) is determined by said combined distance; i) the position of one end of said slot (24) determines the maximum extension of said compressible link (18,21,27) and the position of the other end of said slot (24) arranged to permit free movement of said mechanism between end stops of said butterfly; and j) an actuating link (28) is adapted to be pivotally connected to said mechanism at said third axis (25a). 2. A valve according to claim 1 wherein said compressible link comprises a first member (18) pivoted about said first axis (17a), a second member (21) pivoted about said second axis (22a), and a spring (27) adapted to urge said members (18,21) apart. 3. A valve according to claim 2 wherein said spring (27) is a coiled compression spring, and said members (18,21) include seats (26) to locate said spring. 4. A valve according to claim 3 wherein one of said members (21) is located tel escopical 1 y in the other of said members ( 18) . 5. A valve according to any preceding claim wherein at an intermediate position of said butterfly, said first, second and third axes ( 17a, 22a, 25a) are in a common plane. 6. A valve according to any preceding claim wherein said actuating link (28) is situated between said second and third levers (19,23). 7. A valve according to claim 6 wherein said first and second levers are situated in parallel planes. 8. A valve according to any preceding claim wherein said first, second and third axes ( 17a, 22a, 25a) are perpendicular to the axis of said compressible link (18,21 ,27). 9. A valve according to any preceding claim wherein said compressible link (18,21,27) is situated between said third lever (23) and said first lever (15). 10. A valve according to claim 9 wherein said first and third levers (15,23) are situated in parallel planes.

Inventors: KEEGAN COLM MICHAEL PATRICK, KEEGAN, COLM, MICHAEL, PATRICK
Applicants: KEEGAN COLM MICHAEL PATRICK, WABCO AUTOMOTIVE UK, KEEGAN, COLM, MICHAEL, PATRICK, WABCO AUTOMOTIVE U.K. LIMITED
Application year: 1998
Main classification: F02D9
IPC codes: F02D9, F02D11, F16K31