192 clutches and power-stop control – Clutches – Torque responsive
Reexamination Certificate
1999-07-06
2001-01-09
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Torque responsive
C192S083000, C192S150000
Reexamination Certificate
active
06170627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a safety coupling designed to transfer torque between two machine components sharing the same axis.
2. Description of the Related Art
An exemplification of such a safety coupling is published in the German paper DE-OS-29-23-902. The safety coupling serves to transfer torque between two machine components sharing the same axis, while preventing unacceptably high torque increases. The safety coupling includes at least one thin-walled sleeve, forming a wall of a ring-shaped chamber extending in axial direction. The ring-shaped chamber can be pressurized with a medium in order to elastically deform the sleeve in radial direction, causing it to jam against the surface of an element onto which the coupling is mounted. Adjacent to the ring-shaped chamber are drillings, which are a part of a safety device or coupling relief device. As a result of the relative motion between the surfaces and the actions of the relief mechanism, the pressurized medium residing in the ring-shaped chamber can escape through the drillings, thus lowering the pressure inside the chamber.
To transfer a certain torque level, a certain surface pressure is required. For that purpose, oil is being pumped into the chamber, which is needed to deform the respective machine components relative to one another. In this way, the coupling is adjusted to the desired torque capacity. If, during an overload condition, this torque is exceeded, the coupling slips. The maximum torque level that can be transmitted is lowered because the effective, static friction coefficient transitions into the sliding friction coefficient. There is a relative motion in circumferential direction between the individual elements of the two machine components, which are jammed relative to one another. A shear disk mounted on one machine component shears off a shear valve, opening the connection to the ring-shaped chamber of the coupling. After shearing off the shearing valve (or valves), the pressurized oil can freely expand and the torque to be transmitted reduces to zero within a few milliseconds.
The disadvantage of these types of safety couplings centers around the fact that these couplings respond only when there is a relative motion between the surfaces which are jammed against one another (one of which is formed by the coupling body), or upon or a certain drivetrain-related torsional motion. This can cause permanent, irreparable damage in the drivetrain, which is reflected in an increase in the cost associated with the re-setting of the coupling to its original state as it operated prior to its activation. Furthermore, the relative motion or torsional deformations are directly linked to each other. Thus, the placement of the coupling is restricted to those areas, in which high torque levels should be avoided, thereby limiting the scope of the application of this coupling from the very beginning.
SUMMARY OF THE INVENTION
The present invention provides a safety coupling, of the type mentioned in the introduction, which avoids the disadvantages. An overload safety device for preventing a torque overload condition is cost-effective, easy to manufacture, as well as fast responding. The overload safety device designed to prevent a torque overload condition is effective at torque levels which are only minimally above the maximum allowable torque. The magnitude of the maximum allowable torque to be transmitted is adjusted so that, if this torque is exceeded, the torque transmission can be quickly disrupted. Furthermore, the overload safety device designed to prevent a torque overload condition offers a rapid response time, i.e., a short period of time between the occurrence of an unacceptable high torque level and the interruption of the torque transmission, and is not limited to only the deformation in the drivetrain.
The safety coupling, designed to transfer torque between two machine components sharing the same axis—a first machine component and a second machine component—is placed in a drivetrain and is equipped with a coupling body to frictionally engage the two machine components. The coupling body includes at least one thin-walled sleeve forming a wall of a ring-shaped chamber extending in axial direction. The ring-shaped chamber can be pressurized with a medium. There is at least one supply drilling, extending through the coupling body to the ring-shaped chamber. Sealing valves seal the supply drillings in an air/fluid tight manner. There is also a relief mechanism provided. This relief mechanism includes at least one machine part containing an explosive substance which, in the event of an overload condition, is triggered to explode, allowing the supply drillings to open. The explosive substances are either solid, liquid, or viscid substances or substance mixtures which, after ignition by sparks, flames, or impact, etc., rapidly release large amounts of compressible gases, causing destructive effects in its immediate surroundings.
For the triggering and relief of the coupling and the storage of the explosive substance, there are at least two possibilities. The triggering can occur directly, i.e., the explosive substance is integrated directly in the sealing valves and ignited there. The triggering by the machine element carrying the explosive substance can occur indirectly, i.e., the relief mechanism includes a shear device. The explosive substance is applied to “connectors” and is activated at the site of the shear device.
In the latter mentioned case, conventional shear devices are used, including devices such as the shear disk, for example. The shear disk is placed in a fixed position relative to the coupling body and, when triggered, the disk can be moved in axial or radial direction relative to the coupling body. Additional devices to accelerate this relative motion are feasible. The machine part containing the explosive substance can be designed in the form of separator bolts or explosive bolts, for example. The explosive bolts are placed parallel to the centerline of the driveshaft and are mounted so they can slide in axial direction with respect to the sealing valves. A minimum of three equally-spaced explosive bolts are arranged on the drive shaft. The shear device itself can be mounted in a torsionally rigid manner onto the driveshaft, although it is moveable in axial direction. One possibility of such an arrangement includes the use of a splined shaft connection between the driveshaft and the shear device. The shear device can also be mounted in a freely rotating manner on the drive or driven shaft. A torsionally rigid connection is not necessarily required, although it appears to be a good solution when applied in combination with a shear disk, since the disk with the respective oblong openings can be designed to accommodate the sealing valves, which are frequently designed in the form of valves.
The machine parts containing the explosive substances are coupled with an ignition device which is activated in response to a signal from the coupling. The coupling is in the form of a control unit, including at least one input for actual values and one output. The input or inputs are each connected to a torque sensing/acquisition device which is part of the power take-off drivetrains. The actual value for the current torque is compared with either a fixed or a calibratable maximum allowable torque value stored in the control device. If a deviation occurs, a signal is issued at the output of the control device, initiating the triggering of the relief mechanism, or in this case, the ignition of the explosive bolt. Since the data transfer, the data comparison and the triggering of the relief mechanism occurs at the speed of light, such a safety coupling is especially useful for rapid triggering during a torque overload condition or during any other disturbances. The relief mechanism can be triggered immediately upon recognition of a torque spike or even prior to that event. Mechanical sensing/acquisition devices always have some delays in this regard.
Bonck Rodney H.
Taylor & Aust P.C.
Voith Turbo GmbH & Co. KG
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