192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
2000-04-06
2001-04-03
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C180S170000, C123S399000
Reexamination Certificate
active
06209698
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a wrap spring clutch and more particularly to an electromagnetically actuated wrap spring clutch that is capable of generating a high torque output using a low power input.
2. Disclosure of Related Art
A conventional, electromagnetically actuated, wrap spring clutch includes an output shaft, a shaft hub disposed about the shaft and connected for rotation therewith, and an input hub. The input hub is also disposed about the shaft, but may rotate independently of the shaft when the wrap spring clutch is deenergized. The clutch further includes a coil substantially disposed about the shaft hub and an annular wrap spring disposed about a portion of the input hub and a portion of the shaft hub. A first end of the wrap spring is connected to the input hub so that the spring rotates with the input hub. Energizing the coil establishes magnetic flux circuits or closed loops in the magnetically permeable portions of the clutch. Attractive forces arising from the flux draw a second end of the spring into contact with the shaft hub (which may be non-rotating at this point). Frictional forces restrain the second end of the spring from rotating. The difference in relative rotation between the first and second ends of the spring causes the spring to wrap down upon the shaft hub, thereby transmitting torque from the input hub to the shaft hub and output shaft.
Conventional clutches have long suffered from poor efficiency. The geometry of the magnetically permeable portions of a conventional clutch generally does not permit generation of a sufficient level of magnetic flux in response to relatively low power inputs. A decreased magnetic flux provides less attractive forces internal to the clutch (i.e., between the input and output components of the clutch) which, in turn, results in a diminished torque capacity. The inability to transmit a sufficient level of torque to the output shaft in response to low power inputs renders conventional clutches unsuitable for certain applications, such as automotive applications, where available power is limited as an initial matter, and in which large variations in voltage must be provided for (e.g., as a result of a reduction in the voltage output of a chemical battery during extremely cold weather).
There is thus a need for a wrap spring clutch that minimizes or eliminates one or more of the above-mentioned problems.
SUMMARY OF THE INVENTION
The present invention provides a relatively high efficiency electromagnetically actuated wrap spring clutch. An object of the present invention is to provide a clutch that is capable of generating a high torque output using a low power input to the clutch coil.
An electromagnetically actuated wrap spring clutch in accordance with the present invention includes a shaft assembly, a control assembly and a coil assembly. The shaft assembly includes a shaft extending along a longitudinal axis and a shaft hub disposed radially outwardly of the shaft and mounted to the shaft for rotation therewith. The control assembly includes an input hub that is disposed radially outwardly of the shaft and that is rotatable relative to the shaft. The control assembly also includes an annular control collar having a collar flange portion and a wrap spring that is connected at one end to the control collar and at a second end to the input hub. The input hub, spring, and control collar rotate as a unit about the shaft. The coil assembly includes a housing disposed radially outwardly of the shaft hub and a coil within the housing. The housing has a housing flange portion that is axially adjacent the collar flange portion of the control collar.
In a preferred embodiment, both the collar flange portion and the housing flange portion are perpendicular to the longitudinal axis extending through the shaft. The collar flange portion extends away from the axis while the housing flange portion extends towards the axis. The geometry of the housing flange portion and the collar flange portion insures that a relatively large portion of the surface area of the housing is adjacent a relatively large portion of the control collar. This geometry promotes a high level of magnetic flux transfer between the housing and the control collar—two of the magnetically permeable components in a magnetic flux circuit created when a current is generated in the coil. Moreover, the geometry promotes a high level of magnetic flux transfer between the control collar and the shaft hub. Therefore, even with a low power input, there is a strong attraction between the input components of the clutch, including the control collar—and the input hub it is connected to—and the output components of the clutch, including the shaft hub. A clutch in accordance with the present invention is therefore able to transmit a high level of torque from the input hub to the shaft hub using a low power input.
An advantage of the present invention is that it can be used in applications, such as automotive applications, where available power is limited as an initial matter, and in which large variations in power must be provided for (e.g., as a result of a reduction in the voltage output of a chemical battery during extremely cold weather).
In a preferred application, the inventive clutch may be utilized in a speed control device of a vehicle. Conventional speed control devices employ means, such as a tooth clutch, for selectively transmitting torque from a motor driven input shaft to an output shaft in order to selectively actuate a throttle control. Because return springs bias the throttle control to a predetermined position, the torque transmitted to the output shaft must be sufficient to overcome the biasing force of the return springs. As a result, conventional speed control devices have employed large and/or expensive torque transmitting means to transmit a high level of torque from the input shaft to the output shaft. The present invention, however, is able to transmit a high level of torque despite its relatively small size and weight—thereby representing a significant improvement in the art. In addition, the present invention is able to transmit a high level of torque despite using significantly less electrical power than conventional torque transmitting means.
These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.
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Bonck Rodney H.
Dana Corporation
Dykema Gossett PLLC
Lewis Tisha D.
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