PIVOT ACTUATOR

A pivot actuator (1), comprising: a housing (2); a piston (3) that is supported in the housing (2) and displaceable along a longitudinal axis (7) of the housing; a drive shaft (4) that protrudes from the housing (2) wherein the piston (3) engages the drive shaft (4) by form locking so that the drive shaft (4) is pivoted about a drive axis (8) by a pivot angle (10) to an end position through a displacement of the piston; and a switching cam (11, 26) that is fixed torque proof at the drive shaft (4) and configured to contact a stop element (5) at the housing (2) with a convex stop surface (18) at the switch element, wherein the end position is adjustable by an adjustment angle (25) about the drive axis (8) by displacing the stop element (5) along an adjustment axis (20) transversal to the drive axis (8), characterized in that the stop surface (18) follows an involute (22) of a circle (23) about the drive axis (8) wherein the involute is arranged in a direction transversal to the drive axis (8) so that the circle (23) is tangential to the adjustment axis (20).

The invention relates to a pivot actuator including a housing, a piston that is supported in the housing and displaceable along a longitudinal axis of the housing, a drive shaft that protrudes from the housing, wherein the piston engages the drive shaft by form locking so that the drive shaft is pivoted about a drive axis by a pivot angle to an end position through a displacement of the piston; and a switching cam that is fixed torque proof at the drive shaft and configured to contact a stop element at the housing with a convex contact surface of the switch cam in the end position, wherein the end position is adjustable by an adjustment angle by displacing the stop element along an adjustment axis that is oriented transversal to the drive axis

A generic pneumatic pivot actuator is known e.g. under the product the designation “Keystone Figure 89” by Emerson Electric Co Saint Louis, MI/US. The known pivot actuator has a pivot angle of 90 degrees with two defined end positions that are adjustable by stop screws within an adjustment angle range of 10 degrees respectively. S-shaped contact surfaces contact end surfaces of the stop screws with partial surfaces of the S-shaped contact surfaces that extend transversal to the drive axis. An actuation angle of the known pivot actuator is limited by permissible positions of a contact point of the contact surface in the end surface of the contact screw that varies with the adjustment.

Pivot actuators are known in the art that have flat contact surfaces that are arranged at different angles relative to the drive axis after adjustment and that impact the end surfaces which can damage the contact screws.

Object

Thus, it is an object of the invention to increase the adjustment angle

Solution

Improving upon the known pivot actuator it is proposed according to the invention that the contact surface follows an involute of a circle about the drive axis in a direction transversal to the drive axis wherein the circle contacts the adjustment axis. The involute designates a path of an end point of a line segment that is wound from a circumference of the circle and is always oriented perpendicular to the line segment.

Since the adjustment axis and the line segment are tangents to the circle the contact surface of the pivot actuator according to the invention always impacts the same contact point in the end surface of the contact element in a perpendicular direction. Thus, the adjustment angle is not limited by a size of the end surface but only by the installation space that is usable for the contact surface in a radial direction relative to the drive axis. Thus, a pivot actuator according to the invention can provide an adjustment angle of 25°, 30° or more.

Advantageously the adjustment angle of a pivot actuator according to the invention is adjustable by threading the stop element about the adjustment axis. Adjusting the adjustment angle by stop screws is proven and well known in the art. Further advantageously the stop screw is locked at the housing by a lock nut. Alternatively, the stop element can be fixed by clamping devices or by bonding through gluing or soldering at the housing.

Advantageously the switching cam includes a second stop surface in a pivot actuator according to the invention wherein the second stop surface contacts the second stop element arranged at the housing in a second end position of the switching cam. This pivot actuator according to the invention facilitates an exact adjustment of two end positions of a valve, e.g., open and closed.

Advantageously the drive shaft of a pivot actuator according to the invention includes a teething that supports the switching cam torque proof. This couples a movement of the switching cam and of the drive shaft precisely during operations. On the other hand side, the switching cam which is a wear element can be replaced easily.

Advantageously the teething in the pivot actuator according to the invention is rotation symmetrical. Thus, the switching cam can be connected with the drive shaft in plural precisely defined positions. Further advantageously the teething is 8 times rotation symmetrical. A drive shaft of this type with involute teething is known from applicant's product line “agturn”.

A pivot actuator according to the invention can include spring elements between the housing and the piston that urge the piston into a neutral position in the range of the pivot angle. A pivot actuator of this type according to the invention reverts to a defined position should a failure occur.

Advantageously a pivot actuator according to the invention includes a pressure tight chamber that is defined by the piston and a fluid connection at the chamber, wherein the piston is displaceable by loading the fluid connection with a fluid. A pivot actuator of this type according to the invention can be driven hydraulically of pneumatically. Alternatively, a pivot actuator according to the invention can be driven electromagnetically or mechanically.

Advantageously a pivot actuator according to the invention includes a second pressure tight second chamber defined by the piston and a second fluid connection at the second chamber, wherein the piston is moveable back and forth by loading the second fluid connection. A position of this pivot actuator according to the invention is controllable by a pressure difference between the first fluid connection and the second fluid connection.

Advantageously a pivot actuator according to the invention includes a second piston that is moveable in the housing along the longitudinal axis wherein the second piston engages the drive shaft by form locking so that the drive shaft is pivoted relative to the first piston when the second piston is moved contrary to the first piston The second piston compensates a bending load that is imparted by the first piston upon the drive shaft and causes a symmetrical force transmission between the piston and the drive shaft. Additionally, the second piston doubles an effective surface that transfers force from the fluid without significantly increasing a size of the pivot actuator. Alternatively, a simpler pivot actuator according to the invention can include only one piston.

Ferrous metals or non-ferrous metals and synthetic materials can be used for the switching cam depending on load conditions.

The pivot actuator1according to the invention shown inFIGS.1,2a/band3a/bincludes a housing2, two pistons3included in the housing2and a drive shaft4that protrudes from the housing2and two stop elements5.

The pistons3define one pressure tight chamber6between each other and two pressure tight chambers6in combination with the housing2. The pistons3are displaceable in the housing2counteracting along a longitudinal axis7of the housing2and the driveshaft4is pivotable about a drive axis8.

The pistons3and the driveshaft4include teethings9that engage each other by form locking. Loading the chamber6through non-illustrated pressure connections at the housing2with compressed air moves the pistons3and the drive shaft4is pivoted by the teethings9by a pivot angle10that is illustrated inFIGS.3a/b, between end positions of 0 degrees and 60 degrees.

A switching cam11is attached at the drive axis8in the housing2and illustrated in detail inFIGS.4a/b, and5. The switching cam11has a circular disc shaped base structure with a diameter12of 30 mm and a thickness13of 9 mm and includes an axial receiving opening14. The receiving opening14is shaped as an eight pointed star with rounded corners that fixes the switching cam11on the drive shaft4through a longitudinal teething.

The switching cam11includes two identical discs15that are rotated relative to each other along the drive axis8, that are loosely placed on top of each other and made from the case-hardened material 1.0503/C45 respectively including a radial protrusion16that has a thickness of the switching cam11and a radius17of 24.5 mm. A respective contact surface18is configured at the protrusion.

The stop elements5respectively include a set screw19that is threaded into the housing2along an adjustment axis20and a lock nut21that locks the set screw19at the housing2. The stop surface18follows an involute22about the circle23about the drive axis8wherein the circle23contacts the adjustment axis20. Thus the contact point24in the stop surface18is arranged on the adjustment axis20in each permissible end position.

FIG.5illustrates the switching cam11in the maximum permissible end position and in dashed lines in the minimum permissible end position. The first pivot actuator1has a nominal pivot angle of 90 degrees. Limits for the end position adjustment for the 0 degree end position of the first pivot actuator1are at −5 degrees and +30 degrees, for the 90 degree end position the limits are at 60 degrees and 95 degrees. The adjustment angle25of the switching cam11between the limits of the end position adjustment is 35 degrees.

FIGS.6a/bshow interior views of the end positions for a second pivot actuator according to the invention. The second pivot actuator corresponds to the first pivot actuator besides the switching cam26that is illustrated in detail inFIG.7. Also the switching cam26of the second pivot actuator includes the basic structure and the receiving opening14of the switching cam11of the first pivot actuator1, however the switching cam26of the second pivot actuator is not assembled from discs15but fabricated in one piece.

Two other advantageous pivot actuators differ from the first pivot actuator1according to the invention only in that one of the discs15is pivoted by 45 degrees or 90 degrees about the pivot axis compared to the first pivot actuator1according to the invention. The latter two pivot actuators thus have a nominal pivot angle of 135° or 180°.