TORQUE OVERLOAD INDICATOR  Inventor: Armin E. Jocz, Ada, Mich.  Assignee: Westran Corporation, Sparta, Mich.  Appl. No.: 303,506  Filed: Sep. 18, 1981  Int. Cl.3 ............................................ .. G08B 21/00  U.S. Cl. ............................... .. 340/665; 73/862.31; 340/679  Field of Search ..................... .. 340/665, 688, 679; 73/862.31, 862.49, 862.23  References Cited
2,503,141 4/1950 Stone 4,182,168 l/1980 Desch ............................. .. 73/862.49
Primary Examiner—-Glen R. Swann, III Attorney, Agent, or Firm—Gifford, VanOphem, Sheridan, Sprinkle & Nabozny
A device is provided for use with an actuator having an actuator shaft which indicates when the torque on the
actuator shaft exceeds a predetermined limit. The device comprises a housing which carries a pair of limit switches. A shaft extension is operatively connected with the actuator shaft so that axial force on the actuator shaft, which is proportional to the shaft torque, is transmitted to the shaft extension. A hub and Belleville washer arrangement translates the axial force on a shaft into a proportional axial movement of the hub while a radially extending member from the hub includes a portion positioned adjacent the limit switch. Thus, when the axial force in one direction on the shaft exceeds a first predetermined amount, the radially extending member activates one limit switch which in turn is connected to an indicator. Similarly, when the axial force in the other direction on the shaft exceeds a second predetermined amount, the radially extending member activates the other limit switch which is also connected to the indicator. An adjustable cam is secured to the radially extending member to vary the torque limit at which the limit switch is activated.
TORQUE OVERLOAD INDICATOR
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to indicating devices and, more particularly, to a device for indicating when the torque on a shaft exceeds a predetermined limit.
Description of the Prior Art
Many types of valve actuators include an actuator shaft which is rotatably motor driven in one direction to open the valve and in the opposite direction to close the valve. Furthermore, the actuator shaft is subjected to relatively high torque loads when the valve reaches or is initially moved from either its open or closed position. In the event of valve malfunction, however, the actuator shaft can be subjected to excessive torque loads which can damage the valve components including the valve motor.
There have been a number of previously known devices designed to measure the torque on the actuator shaft to deactivate the valve motor when the torque exceeds a predetermined limit. These previously known devices, however, have not proven wholly satisfactory in use.
One disadvantage of these previously known devices is that they are complex and unreliable in operation. Consequently, these previously known torque limiting devices frequently fail to deactivate the valve motor despite a torque overload thus damaging the valve components.
A still further disadvantage of many of the previously known devices for deactivating the actuator motor at a predetermined torque overload is that the torque limit at which the valve motor is deactivated is not adjustable by the ultimate user but rather is preset at the place of manufacture. In addition, it is conventional to set the torque overload limits just below the maximum permissible limits. Many valves, however, slowly deteriorate during extended operation and the maximum torque applied to the valve actuator shaft also gradually increases with the deterioration of the valve. Finally, the maximum permissible torque is exceeded and at this time, the valve essentially is rendered inoperable. Immediate repair or replacement of the valve is then required before the operation of the fluid system can continue. In many circumstances, however, the immediate replacement or repair of the valve is either impractical or impossible thus resulting in prolonged downtime of the fluid system.
SUMMARY OF THE PRESENT INVENTION
The present invention overcomes the above-mentioned disadvantages by providing a device for use with an actuator, such as a valve actuator, which activates an alarm or other indicator when the torque on the actuator shaft exceeds a predetermined torque limit. This torque limit, however, is less than the maximum permissible torque limit for the valve actuator and is adjustable by the ultimate end user of the ‘valve.
In brief, the device according to the present invention comprises a shaft extension which is coaxial with the actuator shaft and coupled to the actuator shaft by thrust bearings. The thrust bearings cause the shaft extension to move axially with the actuator shaft but without the rotation of the actuator shaft.
A device housing is secured to the housing for the valve actuator and the shaft extension either extends through or adjacent the device housing. At least one and preferably two limit switches are mounted to the device housing.
The axial force, i.e., either compression or tension, of the valve actuator shaft is proportional to the torque applied to the actuator shaft. This axial force, in turn, is transmitted to the shaft extension and means carried on the shaft extension translate this axial force to a proportional axial movement. In the preferred form of the invention, this translating means comprises a hub sandwiched in between two Belleville washer clusters. The outside axial end of each cluster is entrapped between both the device housing and a member or abutment surface carried by the shaft extension. Thus, an axial force on the shaft extension is translated into a proportional axial movement of the hub.
A rod is secured to the hub so that the rod extends radially outwardly from the shaft extension and the rod includes a portion positioned adjacent the limit switch or switches. Thus, axial movement of the hub moves the rod axially with respect to the axis of the shaft extension and activates the limit switch whenever axial displacement of the hub extension exceeds a predetermined limit. The limit switch in turn is electrically connected to an alarm or other indicator to indicate to the operator that the torque applied to the actuator shaft has exceeded a predetermined limit.
In the preferred form of the invention, a cam member is adjustably secured to the rod portion so that the torque maximum at which the limit switches are activated can be adjusted by the user. Preferably, the cam can be adjusted to activate the limit switches when the torque applied to the actuator shaft is in the range from 30% to lO0%_ of the maximum torque rating of the valve.
A second pair of limit switches are also mounted within the device housing adjacent the rod. A fixed cam on the rod selectively activates these second limit switches when the torque on the actuator shaft exceeds the maximum torque rating of the valve actuator. This second pair of switches is preferably coupled to the valve motor to deactivate the valve motor when activated to prevent damage to the valve actuator components and the torque setting is not adjustable by the end user.
BRIEF DESCRIPTION OF THE DRAWING
A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which:
FIG. 1 is a partial longitudinal sectional view illustrating the preferred embodiment of the invention;
FIG. 2 is a view taken substantially along line 2—~2 in FIG. 1;
FIG. 3 is a view taken substantially along line 3-3 in FIG. 1;
FIG. 4 is a longitudinal sectional view similar to FIG. 1 but with parts removed and illustrating the operation of the preferred embodiment of the device of the present invention; and
FIG. 5 is a view similar to FIG. 4 but illustrating a different operation of the present invention.