GB1563080A

GB1563080A - Mechanism for controlling the reciprocating movement of a component

Info

Publication number: GB1563080A
Application number: GB3845/78A
Authority: GB
Original assignee: Creusot Loire SA
Current assignee: Creusot Loire SA
Priority date: 1977-02-04
Filing date: 1978-01-31
Publication date: 1980-03-19
Also published as: FR2379718B1; CH619514A5; IT1156430B; IT7867166A0; FR2379718A1; DE7803252U1; DE2804715A1

Description

(54) IMPROVEMENTS IN AND RELATING TO A MECHANISM FOR CONTROL LING THE RECIPROCATING MOVEMENT OF A COMPONENT (71) We, CREUSOT-LOIRE a French Corporate Body of 42, rue d'Anjou, 75008 Paris, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a mechanism for controlling the reciprocating movement of a component along one direction and is especially applicable to the control of valves or gates such as, for example, the admission or readmission valves of turbo-machines.

Turbo-machines comprise a large number of valves for the admission or readmission of gases, and mechanisms for controlling the opening and closing of the valves in accordance with the operation of the machine. In general, each valve is controlled by a rod which is mounted for sliding movement in one direction and is articulated at one end on a lever which is mounted so as to swing about a fulcrum. The reciprocating swinging motion of the lever is determined by a suitable control means, for example by a servomotor. As the end of the lever describes an arc of a circle, the control rod is frequently articulated in order to provide the necessary clearance.

In such systems, the ratio of the lever arms is constant, whatever the position of the mechanism may be, and the lifting or lowering motion of the valve is uniform. If it is desired to vary the lifting or lowering speed of the valve in order to damp the opening or closing motion, it is necessary to vary the speed by means of cams, and this complicates the installation. Furthermore, the force required to move the valve is greater when it is desired to cause the valve to disengage from its seat, the force required to move the valve being smaller when the latter is already open. It would therefore be useful to vary the force transmitted to the control rod of the valve in accordance with the position of the latter.

According to the invention there is provided a mechanism for controlling reciprocatory movement of a component in one direction, comprising a control rod, which is mounted for sliding movement in the direction of movement of the component and is articulated at one end on a lever mounted to swing about a fulcrum on a fixed support, and means for controlling reciprocating swinging movement of the lever, wherein the lever bears on the fixed support through a convex curved bearing surface which is adapted to roll without sliding, over a concave tracking surface provided on the fixed support, the tracking surface having a radius of curvature which is double that of the bearing surface, and being centred on the direction of sliding movement of the rod and the point of contact of the bearing surface on the tracking surface constituting the fulcrum of the lever at all times.

In a preferred embodiment, the bearing surface and the tracking surface are provided on circumferences of the lever and fixed support respectively.

According to a particular embodiment, the bearing surface of the lever and the tracking surface are provided with interengaging circular teeth.

The invention will be more fully understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic view, in elevation, of an embodiment of a mechanism according to the invention; Figure 2 is a section along the line II-II of Figure 1; and Figure 3 is a graph showing the variation of the available driving force as a function of the movement.

A valve 1 for closing an orifice in a yoke 2 is shown in Figure 1. Lifting of the valve 1 is controlled by a rod 10 mounted for sliding movement in a direction 11. The upper end of the rod 10 is articulated on a lever 3 bearing on a fixed support 4 which is firmly fixed to the yoke 2. The lever 3 bears on support 4 through a convex bearing surface 30 which is capable of rolling, without sliding, over a concave tracking surface 40 provided on the fixed support 4.

In the embodiment shown in Figures 1 and 2, the surface 30 comprises two circular tracks of radius r between which are arranged concentric teeth 31 having a primitive circle which is also of radius r. In an analogous manner, the tracking surface 40 comprises two circular tracks having a radius which is double that of the tracks 30 on which they roll. Teeth 41, the primitive circle of which also has a radius 2r, which is double that of the teeth 31 with which they engage, are placed between the tracks 40. As a result, when the tracks 30 roll over the tracks 40, the teeth engage on one another and rolling occurs without sliding.

The motion of the lever 3 is controlled by a servo-motor 5 by means of a rod 50, the end of which is articulated on the lever 3. The servo-motor 5 can be a simple jack, the piston of which controls reciprocating motion of the lever. The centre of the tracking surface 40 is at 42 on the direction 11 of movement of the valve, and the rod 50 of the servomotor reciprocates in a direction 51 which also passes through the centre 42 of the surface 40.

When the valve 1 is in the low closing position, shown in Fig. 1, the lever 3 is in a position in which the centre 32 of the bearing surface 30 lies on the direction 11 of movement of the valve.

It is known that, when the radii of two circumferences which roll over each other are in the ratio 1/2, the hypocycloid described by a point on the circumference of smaller diameter is reduced to a diameter of the external circumference. Thus the point of articulation 12 of the rod 10 on the lever 3, which point is situated on the primitive circle of the teeth 31, will move along the direction 11. In the same way, the point of articulation 52 of the rod 50 of the servo-motor, which point is also situated on the primitive circle of the teeth 31, moves along the direction 51 and passes through the centre 42 of the tracking surface 40.

When the servo-motor 5 imparts a recip rocating motion to the rod 50, the lever 3 therefore swings about the point of contact of the bearing surface 30 with the tracking sur face 40, and this point moves along the arc of the circle of surface 40. In theory, the lever can swing until the point of articulation 52 of the rod 50 is at B on the circle of surface 40.

However, the radii of the tracking surface 40 and of the bearing surface 30 of the lever are chosen such that the valve 1 reaches its upper position when the point of contact between the bearing surface 30 and the tracking surface 40 is at E, in the middle of the arc AB, shown by the dot-and-dash line in Figure 1. In this position, the ratio between the lever arms is equal to 1.

Thus, starting from the position shown in Figure 1, the servo-motor pulls on the lever 3 and the force transmitted to the valve is therefore multiplied by a very large ratio of the lever arms. It is precisely at this moment that the force required to disengage the valve from its seat is greatest. On the other hand, as shown on the graph of Figure 3, the driving force available on the control rod 10 decreases as a function of the lift of the valve which has been indicated on the abscissa; the ratio of the lever arms, which is indicated on the ordinate, gradually decreases to 1.

In the opposite direction, the closing speed of the valve decreases as the latter approaches its seat, because of this movement of the fulcrum of the lever from E to A along the surface 40. The desired damping effect is thus obtained on contact between the components.

In order that the movable bearing surface rolls, without sliding, over the fixed tracking surface, it is not necessary to use a set of teeth, and other systems, such as chains or belts, can provide analogous results.

It will be appreciated that the mechanism could simultaneously actuate the opening of several valves which are driven by the same lever or by a pair of levers actuated simultaneously.

There is thus provided a very simple mechanism which makes it possible to vary the force transmitted by the mechanism in accordance with the position of the mechanism.

WHAT WE CLAIM IS: 1. A mechanism for controlling reciprocatory movement of a component in one direction, comprising a control rod, which is mounted for sliding movement in the direction of movement of the component and is articulated at one end on a lever mounted to swing about a fulcrum on a fixed support, and means for controlling reciprocating swinging movement of the lever, wherein the lever bears on the fixed support through a convex curved bearing surface which is adapted to roll, without sliding, over a concave tracking surface provided on the fixed support, the tracking surface having a radius of curvature which is double that of the bearing surface and being centred on the direction of sliding of the rod, and the point of contact of the bearing surface on the tracking surface constituting the fulcrum of the lever at all times.

2. A mechanism according to claim 1, wherein the bearing surface and the tracking surface are provided on circumferences of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. controlled by a rod 10 mounted for sliding movement in a direction 11. The upper end of the rod 10 is articulated on a lever 3 bearing on a fixed support 4 which is firmly fixed to the yoke 2. The lever 3 bears on support 4 through a convex bearing surface 30 which is capable of rolling, without sliding, over a concave tracking surface 40 provided on the fixed support 4. In the embodiment shown in Figures 1 and 2, the surface 30 comprises two circular tracks of radius r between which are arranged concentric teeth 31 having a primitive circle which is also of radius r. In an analogous manner, the tracking surface 40 comprises two circular tracks having a radius which is double that of the tracks 30 on which they roll. Teeth 41, the primitive circle of which also has a radius 2r, which is double that of the teeth 31 with which they engage, are placed between the tracks 40. As a result, when the tracks 30 roll over the tracks 40, the teeth engage on one another and rolling occurs without sliding. The motion of the lever 3 is controlled by a servo-motor 5 by means of a rod 50, the end of which is articulated on the lever 3. The servo-motor 5 can be a simple jack, the piston of which controls reciprocating motion of the lever. The centre of the tracking surface 40 is at 42 on the direction 11 of movement of the valve, and the rod 50 of the servomotor reciprocates in a direction 51 which also passes through the centre 42 of the surface 40. When the valve 1 is in the low closing position, shown in Fig. 1, the lever 3 is in a position in which the centre 32 of the bearing surface 30 lies on the direction 11 of movement of the valve. It is known that, when the radii of two circumferences which roll over each other are in the ratio 1/2, the hypocycloid described by a point on the circumference of smaller diameter is reduced to a diameter of the external circumference. Thus the point of articulation 12 of the rod 10 on the lever 3, which point is situated on the primitive circle of the teeth 31, will move along the direction 11. In the same way, the point of articulation 52 of the rod 50 of the servo-motor, which point is also situated on the primitive circle of the teeth 31, moves along the direction 51 and passes through the centre 42 of the tracking surface 40. When the servo-motor 5 imparts a recip rocating motion to the rod 50, the lever 3 therefore swings about the point of contact of the bearing surface 30 with the tracking sur face 40, and this point moves along the arc of the circle of surface 40. In theory, the lever can swing until the point of articulation 52 of the rod 50 is at B on the circle of surface 40. However, the radii of the tracking surface 40 and of the bearing surface 30 of the lever are chosen such that the valve 1 reaches its upper position when the point of contact between the bearing surface 30 and the tracking surface 40 is at E, in the middle of the arc AB, shown by the dot-and-dash line in Figure 1. In this position, the ratio between the lever arms is equal to 1. Thus, starting from the position shown in Figure 1, the servo-motor pulls on the lever 3 and the force transmitted to the valve is therefore multiplied by a very large ratio of the lever arms. It is precisely at this moment that the force required to disengage the valve from its seat is greatest. On the other hand, as shown on the graph of Figure 3, the driving force available on the control rod 10 decreases as a function of the lift of the valve which has been indicated on the abscissa; the ratio of the lever arms, which is indicated on the ordinate, gradually decreases to 1. In the opposite direction, the closing speed of the valve decreases as the latter approaches its seat, because of this movement of the fulcrum of the lever from E to A along the surface 40. The desired damping effect is thus obtained on contact between the components. In order that the movable bearing surface rolls, without sliding, over the fixed tracking surface, it is not necessary to use a set of teeth, and other systems, such as chains or belts, can provide analogous results. It will be appreciated that the mechanism could simultaneously actuate the opening of several valves which are driven by the same lever or by a pair of levers actuated simultaneously. There is thus provided a very simple mechanism which makes it possible to vary the force transmitted by the mechanism in accordance with the position of the mechanism. WHAT WE CLAIM IS:

1. A mechanism for controlling reciprocatory movement of a component in one direction, comprising a control rod, which is mounted for sliding movement in the direction of movement of the component and is articulated at one end on a lever mounted to swing about a fulcrum on a fixed support, and means for controlling reciprocating swinging movement of the lever, wherein the lever bears on the fixed support through a convex curved bearing surface which is adapted to roll, without sliding, over a concave tracking surface provided on the fixed support, the tracking surface having a radius of curvature which is double that of the bearing surface and being centred on the direction of sliding of the rod, and the point of contact of the bearing surface on the tracking surface constituting the fulcrum of the lever at all times.

the lever and the fixed support respectively.

3. A mechanism according to either claim 1 or claim 2, wherein the bearing surface and the tracking surface are provided with interengaging teeth, the primitive cir cles of which coincide with the corresponding surfaces.

4. A mechanism according to claim 3, wherein the lever is provided, adjacent the teeth, with at least one circular track bearing on a corresponding track provided on the fixed support adjacent the teeth thereof, the tracks each having a diameter which is equal to the primitive diameter of the corresponding teeth.

5. A mechanism according to any one of claims 1 to 4, wherein the means for controlling the reciprocating motion movement of the lever comprises a jack, the rod of which is articulated on the lever and extends along a radius of the tracking surface.

6. A mechanism for controlling reciprocatory movement of a component substantially as herein described with reference to the accompanying drawings.