WO2010070414A2

WO2010070414A2 - Protection device for viscous clutch

Info

Publication number: WO2010070414A2
Application number: PCT/IB2009/007750
Authority: WO
Inventors: Bastian Brand; Ulrich Stirnkorb; Thomas Schambock
Original assignee: Horton, Inc.
Priority date: 2008-12-15
Filing date: 2009-12-14
Publication date: 2010-06-24
Also published as: WO2010070414A3

Abstract

A viscous clutch assembly includes an input member, an output member, a reservoir for holding a shear fluid, a working chamber for accepting the shear fluid to selectively rotationally engage the input member and the output member for the transmission of torque therebetween, a valve assembly for controlling flow of the shear fluid to the working chamber, an electromagnet for actuating the valve assembly, a protection member configured to be moveable as a function of centrifugal force produced by rotation of the input member during clutch operation to reduce flow of the shear fluid to the working chamber at or above a first rotational speed, and a biasing member for biasing the protection member toward a position that allows flow of the shear fluid to the working chamber. The centrifugal force produced by rotation of the input member acts against a biasing force of the biasing member.

Description

PROTECTION DEVICE FOR VISCOUS CLUTCH

BACKGROUND

The present invention relates to viscous clutches, and more particularly to control mechanisms for viscous clutches.

Viscous clutches are, for example, known for automobile applications, such as for selectively rotating a fan used to cool an engine. In a typical viscous clutch, a shear fluid is provided in a reservoir. The viscous fan clutch operates by selectively introducing the shear fluid from the reservoir to a working chamber to frictionally engage two components, such as a driven rotor connected to a drive input and an output member connected to the fan, by transmitting torque through the shear fluid. Such a viscous clutch tends to engage rotation of the fan when shear fluid is present in the working chamber and to disengage rotation of the fan when the shear fluid is removed from the working chamber. By selectively controlling the amount of shear fluid in the working chamber, a rotational output speed of the clutch can be controlled to, in turn, control a rotational speed of the fan. Many known viscous clutches, such as that described in PCT Published Application No. WO 2007/016497 Al, are electromagnetically actuated with an electromagnetic coil that can generate magnetic flux to control the operation of a valve that, in turn, regulates flow of shear fluid from the reservoir to the working chamber. Overheating can be a problem for viscous clutches. For instance, when an engine providing torque to a viscous clutch operates at relatively high speeds, the clutch may generate excessive amounts of heat that may be damaging to the clutch. Furthermore, relatively high input speeds can expose the viscous clutch drive side (including an input belt, pulleys, etc.) to undesirable torque overload and can expose the fan to over speed damage and produce excessive noise.

A known device to protect a viscous clutch from overheating is shown in FIG. 1 , and includes a rotor 20, a reservoir 21 , a working chamber 22 formed between the rotor and an output member, and a valve assembly 23 controlled by a bimetallic element. The overheating device is a lever 31 positioned over the inlet bore 30 to the working chamber, which is held open by a spring 32. The lever 31 is mounted in a way that the centrifugal force produced when the rotor 20 is rotating acts against the spring force of the spring 32 and closes the inlet bore 30 to the working chamber 22 at a desired speed. Closing the inlet bore 30 with the lever 31 disengages the fan clutch and protects the fan

1

CONFIRWiATlON COPY clutch from overheating at high input speeds. A similar concept is disclosed in U.S. Pat. No. 3,983,980 (claiming priority to DE 23 53 461).

SUMMARY

A viscous clutch assembly according to the present invention includes an input member, an output member, a reservoir for holding a shear fluid, a working chamber for accepting the shear fluid to selectively rotationally engage the input member and the output member for the transmission of torque therebetween, a valve assembly for controlling flow of the shear fluid to the working chamber, an electromagnet for actuating the valve assembly, a protection member configured to be moveable as a function of centrifugal force produced by rotation of the input member during clutch operation to reduce flow of the shear fluid to the working chamber at or above a first rotational speed, and a biasing member for biasing the protection member toward a position that allows flow of the shear fluid to the working chamber. The centrifugal force produced by rotation of the input member acts against a biasing force of the biasing member. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior art clutch.

FIG. 2 is a perspective view of a viscous clutch according to the present invention, shown partially cut away to reveal interior components.

FIG. 3 is a cross sectional view of the viscous clutch, taken along line 3-3 of FIG. 2.

FIG. 4A is an elevation view of a portion of the viscous clutch showing a protection device in a first position.

FIG. 4B is another elevation view of a portion of the viscous clutch showing the protection device in a second position. FIG. 5 is an elevation view of another embodiment of a protection device.

FIG. 6 is a graph of test data illustrating operation of the protection device of the present invention.

While the above-identified drawing figures set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale. Like reference numbers have been used throughout the figures to denote like parts.

DETAILED DESCRIPTION

The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/201,797, entitled "Protection Device For A Viscous Clutch With Reservoir In The Rotor" by Bastian Brand, Ulrich Stirnkorb and Thomas Schambock filed December 15, 2008, and to U.S. Provisional Patent Application Ser. No. 61/204,379, entitled "Protection Device For Use With Viscous Clutch With Reservoir In The Rotor" by Bastian Brand, Ulrich Stirnkorb and Thomas Schambock filed January 6, 2009, both of which are hereby incorporated by reference in their entireties.

In general, the present invention provides a protection device for a viscous clutch that operates as a secondary control for the flow of a shear fluid within the clutch such that when an input speed is at or above a selected speed the clutch is at least partially disengaged (e.g., fully disengaged, or partially disengaged such that output speed is lowered to a safe level). More specifically, the present invention relates to a clutch that provides for selective viscous engagement between input and output members by way of the introduction of the shear fluid to a working chamber defined between the input and output members. A valve assembly operated by selectively energizing an electromagnet provides primary control of the flow of the shear fluid from a reservoir to the working chamber. The protection device is a secondary, mechanical control that is separate from the primary, electromagnetically operated valve assembly. The protection device includes a member that is moveable as a function of centrifugal force generated during operation of the clutch such that at or above the selected speed the protection device can reduce or entirely stop the flow of the shear fluid from the reservoir to the working chamber. In that way, the protection device can override the primary, electromagnetically controlled valve assembly.

FIG. 2 is a perspective view of a viscous clutch 100, shown partially cut away to reveal interior components, and FIG. 3 is a cross sectional view of the viscous clutch 100, taken along line 3-3 of FIG. 2. The viscous clutch 100 includes a shaft 102, a rotor 104, a housing portion 106, a housing cover 108, an electromagnetic coil 110, a reservoir 112, a valve assembly 114, and an inlet bore 116. As shown in the illustrated embodiment, the rotor 104 is fixed to the shaft 102 and provides a rotational input to the clutch 100. Input torque to the clutch 100 can be provided from a belt or shaft (not shown). The housing portion 106 and the housing cover 108 surround the rotor 104, and a working chamber 118 is defined therebetween where a shear fluid can be introduced to provide a viscous engagement to transmit torque from the rotor 104 to the housing portion 106 and the housing cover 108. The housing portion 106 and the housing cover 108 provide an output for the clutch 100, and can be connected to a fan or other component for selective rotation. The reservoir 112 is carried by the rotor 104 and can store the shear fluid when not in active use. The inlet bore 116 is positioned between the reservoir 112 and the working chamber 118 and defines an opening through which the shear fluid passes to exit the reservoir 112 and pass to the working chamber 118. The valve assembly 114 is configured to selectively cover and uncover the inlet bore 116 to selectively control flow of the shear fluid from the reservoir 112 to the working chamber 118 and thereby selectively control engagement of the clutch 100. In the illustrated embodiment, the valve assembly 114 is positioned to selectively cover the right-hand side of the inlet bore 116 as shown in FIG. 3.

The coil 110 can be selectively energized in a conventional manner to generate a magnetic field that can move the valve assembly 114. In one embodiment, the valve assembly 114 is configured to uncover the inlet bore 116 by default, and the coil 110 can be energized to move the valve assembly 114 to cover the inlet bore 116. Such a configuration allows the clutch 100 to be engaged by default, providing a "fail on" configuration that permits the shear fluid to pass the valve assembly 114 in the event of a failure (e.g., a loss of electrical power to the coil 110). The viscous clutch 100 further includes a protection device 130 that is mounted within the reservoir 112 to provide overspeed protection to the clutch 100 independent from operation of the valve assembly 114 and the coil 110. FIG. 4A is an elevation view of a portion of the viscous clutch 100 showing the protection device 130 in a first position, and FIG. 4B is another elevation view of a portion of the viscous clutch 100 showing the protection device 130 in a second position. In the embodiment shown in FIGS. 4A and 4B, the device 130 includes a mounting plate 132, a post 134 having a notch 136, a spring 138, an arm member 140, a first stop 142, a second stop 144, and a fastener 146. The protection device 130 is positioned at an opposite side of the inlet bore 116 from a portion of the valve assembly 114 that can selectively cover the inlet bore 116. The mounting plate 132 can be substantially planar, and provides a support base for the device 130. The inlet bore 116 passes through the mounting plate 132, in other words, the inlet bore 116 includes an opening in the mounting plate 132. The fastener 146, which can be a threaded fastener like a bolt or screw, can secure the mounting plate 132 to the reservoir 112, which in turn is attached to the rotor 104. In the illustrated embodiment, both the reservoir 112 and the device 130 rotate with the rotor 104 during operation of the clutch 100. The post 134 extends from the mounting plate 132, and the notch 136 is formed at a distal end of the post 134 opposite the mounting plate 132. In the illustrated embodiment, the spring 138 is configured as a helical torsion spring with a first end 148 and a second end 150, though other types of springs can be utilized in alternative embodiments. The first end 148 of the spring 138 is engaged with the notch 136 in the post 134. The second end 150 of the spring 138 is engaged with a flange 152 on the arm member 140. The spring 138 is thereby operatively engaged between the post 134 and the arm member 140, and biases the arm member 140 relative to the post 134, the mounting plate 132 and the inlet bore 116. The first and second stops 142 and 144 each extend from the mounting plate 132. The first stop 142 is spaced from the inlet bore 116, and the second stop 144 is located adjacent to the inlet bore 116. In the illustrated embodiment, the inlet bore 116 is positioned between the first and second stops 142 and 144, and close to the second stop 144. The arm member 140 can be pivotally connected to the post 134 such that a distal end of the arm member 140 can rotate about the post 134. A notch 154 is formed in the arm member 140.

The device 130 is mounted in such a way that during operation of the clutch 100 the arm member 140 can move within a limited range. The arm member 140 can be moved to at least partially cover the inlet bore 1 16 or can completely uncover the inlet bore 116. The device 130 holds the arm member 140 in the first, open (i.e., uncovered) position in a normal, default operating condition, as shown in FIG. 4A. In the first, open position, the arm member 140 is biased by the spring 138 into contact with the first stop 142. At increasing input speeds to the rotor 104, centrifugal force on the device 130 increases. When the input speed reaches a given level and the centrifugal force on the device 130 reaches or exceeds a threshold, the device 130 is activated and the arm member 140 moves against the biasing force of the spring 138 to at least partially cover the inlet bore 116 and thereby completely or partially disengages the clutch 100. The threshold for activation and deactivation of the device 130 can be set as a function of a pre-load force of the spring 138. The second, closed (i.e., covered) position of the device 130, when the centrifugal force on the device 130 is above the threshold, is shown in FIG. 4B. In the second, closed position, the arm member 140 contacts the second stop 144. In the illustrated embodiment, the arm member 140 completely covers the inlet bore 116 when in the second, closed position. The second stop 144 can contact the notch 154 in the arm member 140 to help arm member 140 completely cover the inlet bore 116. In alternative embodiments, the notch 154 can be omitted or reconfigured, and/or the second stop 144 repositioned, such that the arm member 140 contacts the stop 144 while only partially covering the inlet bore 116. A spring constant, spring preload and pivot point of the arm member 140 can be configured in such a way that movement of the arm member 140 is not proportional to the centrifugal force when the speed exceeds the threshold, but rather the arm member 140 rapidly moves to its end position at the second stop 144 — it "snaps" when activated. This snapping action is helpful to achieve a fast disengagement and to prevent the clutch 100 from overheating while the output speed is going down. When the input speed to the rotor 104 decreases below the given level and the centrifugal force falls below a threshold, the device 130 is deactivated and the spring 138 returns the arm member 140 to the first position to completely uncover the inlet bore 116.

As shown in the illustrated embodiment, the protection device 130 can be provided in addition to another, primary fan clutch control mechanism (i.e., an electromagnetic control mechanism provided by the coil 110 and the valve assembly 114) and can function to override the primary clutch control mechanism at high rotational input speeds. Below the defined threshold input speed, operation of the clutch 100 can be controlled in a normal manner by the primary clutch control mechanism. The protection device 130 also provides a purely mechanical fail safe function, and can operate when the primary clutch control mechanism is unavailable to regulate the operation of the clutch 100.

It should be noted that the viscous clutch 100 of the illustrated embodiment is shown merely by way of example and not limitation. The protection device 130 can be utilized with nearly any type of viscous clutch, such as that described in PCT Published Application No. WO 2007/016497 Al, which is hereby incorporated by reference in its entirety.

FIG. 5 is an elevation view of another embodiment of a protection device 130', shown in a closed position. The device 130' is configured and operates similar to the device 130 discussed above. However, the device 130' further includes an opening 156 in the arm member 140. The opening 156 is arranged to align with the inlet bore 116 when the arm member 140 is in the closed position in contact with the second stop 144, such that the inlet bore 116 is only partially covered or blocked. In that way, the opening 156 provides a relatively small fluid path through the arm member 140 to allow some shear fluid to pass through inlet bore 116 from the reservoir 112 when the device 130 is activated. The device 130 can thus reduce the amount of shear fluid in the working chamber 118, but still allow for some shear fluid to pass to the working chamber 118 to engage the clutch 100 at a relatively low output speed. Where the clutch 100 is used as a fan clutch, this allows the device 130' to lower an output fan speed to a desired level when the input speed is at or above a defined level. In an alternative embodiment, the opening 156 can be positioned at an edge of the arm member 140 like a notch.

EXAMPLE A test was conducted using the embodiment of the protection device 130 described above with a fan connected thereto. FIG. 6 is a graph of test data illustrating operation of the protection device 130. In the test, the clutch 100 was in a room with an ambient temperature of about 20-30⁰C, and an air blower was positioned to direct hot air at a temperature of approximately 6O⁰C at the clutch 100. Initially, the input to the clutch 100 was maintained at a generally constant speed (i.e., the speed of a rotational input to the clutch) and the electromagnetic coil 110, which provides the primary control of the clutch 100, was cycled on and off and then left in an "on" or energized condition for the remainder of the test. The on/off control of the coil 110 is shown in the graph of FIG. 6 by a pulse width modulation (PWM) duty plot 200 (shown as a dashed line), with a zero value along the vertical access representing the "on" condition. The input speed to the clutch 100 is shown by an input speed plot 202 (shown as a solid line). The graph shows a fan speed plot 204 (shown with a heavy line) illustrating an output speed produced by the clutch 100. As shown in the graph of FIG. 6, the on/off cycling of the primary clutch control (plot 200) at a constant input speed (plot 202) over approximately the first five minutes of the test produced corresponding changes in the fan speed (plot 204), with the fan speed plot 204 dropping close to zero as the PWM duty plot 200 cycled to an "off condition. Next, the input speed was increased in a generally linear fashion and then decreased in a generally linear fashion, with the peak input speed occurring just over 20 minutes into the test. As the input speed was increased to the peak (or relative maximum), the protection device 130 was activated and overrode the primary clutch control (i.e., the coil 1 10 and the valve assembly 114) approximately 16 minutes into the test and limited the output speed to the fan (plot 204) to a fluctuating but near-zero speed until about 28 minutes into the test when the input speed (plot 202) had been reduced to a point sufficient to deactivate the protection device 130. Because the primary clutch control remained in an "on" condition, deactivation of the protection device 130 caused the clutch 100 to re-engage and provide an output to the fan (plot 204) close to the input speed (plot 202).

It will be recognized that the present invention provides numerous advantages and benefits. For example, reducing the output fan speed over the defined input speed level according to the present invention helps limit a maximum power dissipation of the fan clutch, which helps protect the fan clutch from damage and wear from overheating, which can lead to breakdown of shear fluid, bearings, etc. Reducing the fan speed over a defined input speed level helps protect the fan clutch drive side, including the belt, pulleys, etc., from torque overload. Torque overloading presents a risk of drive belt failure, particularly where high input speeds cause the belt to slip, leading to wear and overheating. Belt wear is a cumulative problem in the sense that belt wear accrues over time toward belt failure. Furthermore, reducing the fan speed over a defined input speed level helps protect the fan itself from over speed damage and wear. In addition, reducing the fan speed over a defined input speed level helps reducing a maximum noise level generated by the fan. The protection device of the present invention operates in a passive manner without the need for active control. The present invention works independently from the primary, electromagnetic control system of the fan clutch, and even if the primary clutch control has a total failure or otherwise is inoperable — such as from a loss of electrical power — the clutch maintains fail safe operation (i.e., the fan clutch defaults to engagement in a failure mode) and at the same time continues providing over speed protection. Such fail safe operation provided by the present inventions allows the primary clutch control to default to clutch engagement while still providing the clutch with over speed protection.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. For example, a reservoir in a clutch according to the present invention can be located on either the drive or output side of a driven input disk. Furthermore, a protection device according to the present invention can be utilized with a viscous clutch of nearly any configuration. Moreover, an arm member of a protection device of the present invention can be configured to move pivotally, linearly (i.e., with a translating movement), etc.

Claims

CLAIMS:

1. A viscous clutch assembly comprising: an input member for providing a torque input; an output member; a reservoir for holding a shear fluid; a working chamber defined between the input member and the output member for accepting at least a portion of the shear fluid to selectively rotationally engage the input member and the output member for the transmission of torque therebetween; a valve assembly for controlling flow of the shear fluid from the reservoir to the working chamber; an electromagnet for selectively actuating the valve assembly; a protection member configured to be moveable as a function of centrifugal force produced by rotation of the input member during clutch operation to reduce flow of the shear fluid to the working chamber at or above a first rotational speed; and a biasing member for biasing the protection member toward a position that allows flow of the shear fluid to the working chamber, wherein the centrifugal force acting upon the protection member acts against a biasing force of the biasing member.

2. The viscous clutch assembly of claim 1 , wherein the protection member is carried by the input member, and wherein the centrifugal force acts directly upon the protection member.

3. The viscous clutch assembly of claim 1, wherein the protection member is pivotally moveable.

4. The viscous clutch assembly of claim 1, wherein the biasing member is a torsion spring.

5. The viscous clutch assembly of claim 1, wherein the protection member comprises a plate member pivotally mounted to a post, and wherein the torsion spring is positioned about the post and operatively engaged between the post and the protection member.

6. The viscous clutch assembly of claim 5 and further comprising: a mounting plate, wherein the post is secured to the mounting plate, and wherein the mounting plate is carried by the input member.

7. The viscous clutch assembly of claim 1 and further comprising: an inlet bore in fluid communication with the reservoir and the working chamber, wherein the protection member is moveable to selectively uncover and at least partially cover the inlet bore; and a stop extending from the mounting plate, wherein the stop is configured to contact the protection member to align the protection member relative to the inlet bore when the protection member at least partially covers the inlet bore.

8. The viscous clutch assembly of claim 7, wherein the protection member includes a notch configured to engage the stop when the protection member contacts the stop.

9. The viscous clutch assembly of claim 1, wherein the reservoir is carried by the input member.

10. The viscous clutch assembly of claim 1 and further comprising: an inlet bore in fluid communication with the reservoir and the working chamber, wherein the protection member is moveable to selectively uncover and at least partially cover the inlet bore.

11. The viscous clutch assembly of claim 10, wherein the protection member is positioned at an opposite side of the inlet bore from a portion of the valve assembly that selectively covers the inlet bore, and wherein the protection member is mounted substantially within the reservoir.

12. The viscous clutch assembly of claim 10, wherein the protection member completely covers the inlet bore when in an activated position to substantially prevent shear fluid flow through the inlet bore.

13. The viscous clutch assembly of claim 1 and further comprising: an opening in the protection member for allowing a limited shear fluid flow through protection member.

14. A method of controlling a viscous fan clutch: rotating an input member; energizing an electromagnet as a function of cooling demand to control a valve mechanism to allow flow of a shear fluid to a working chamber located adjacent to the input member; rotating a fan output when the shear fluid is present in the working chamber; and moving a protection member solely as a function of centrifugal force produced by rotation of the input member to at least partially restrict flow of the shear fluid to the working chamber while the valve mechanism is positioned to allow flow of the shear fluid to the working chamber.

15. The method of claim 14 and further comprising: biasing the protection member to a position that does not restrict flow of the shear fluid to the working chamber.

16. The method of claim 15, wherein the protection member is moved by centrifugal force produced by rotation of the input member against biasing of the protection member.

17. The method of claim 14, wherein the protection member at least partially restricts flow of the shear fluid to the working chamber at or above a first rotational speed of the input member.

18. A viscous clutch assembly comprising: an input disk for providing a torque input; an output member surrounding the input disk; a reservoir for holding a shear fluid, the reservoir carried by the input disk to rotate therewith; a working chamber defined between the input disk and the output member for accepting at least a portion of the shear fluid from the reservoir to selectively rotationally engage the input disk and the output member for the transmission of torque therebetween; a bore fluidically positioned between the reservoir and the working chamber; a valve assembly for controlling flow of the shear fluid from the reservoir to the working chamber through the bore; an electromagnet for selectively actuating the valve assembly; and a protection assembly comprising: a mounting plate secured to the input disk; a moveable member carried by the mounting plate and configured to be moveable at or above a first rotational speed of the input disk as a function of centrifugal force from rotation of the input disk to reduce flow of the shear fluid through the bore to the working chamber; and a biasing member for biasing the moveable member relative to the mounting plate, wherein the centrifugal force acting upon the protection member acts against a biasing force of the biasing member.

19. The viscous clutch assembly of claim 18, wherein the moveable member is configured to be pivotally moveable.

20. The viscous clutch assembly of claim 18, wherein the biasing member is a torsion spring.

21. The viscous clutch assembly of claim 18, wherein the protection assembly further comprises: a post extending from the mounting plate, and wherein the biasing member is operatively engaged between the post and the moveable member.

22. The viscous clutch assembly of claim 18 and further comprising: a stop extending from the mounting plate, wherein the stop is configured to contact the moveable member to align the moveable member relative to the bore when the moveable member at least partially covers the bore.

23. The viscous clutch assembly of claim 22, wherein the moveable member includes a notch configured to engage the stop when the moveable member contacts the stop.

24. The viscous clutch assembly of claim 18, wherein the protection assembly is mounted substantially within the reservoir.

25. The viscous clutch assembly of claim 18, wherein the moveable member completely covers the inlet bore when in an activated position to substantially prevent shear fluid flow through the bore.

26. The viscous clutch assembly of claim 18 and further comprising: an opening in the protection member for allowing a limited shear fluid flow to the bore through protection member.

27. A protection device assembly for use with a viscous clutch, the assembly comprising: a mounting plate; a bore defined through the mounting plate; a moveable member carried by the mounting plate and configured to be moveable as a function of centrifugal force to at least partially cover the bore; a spring for biasing the moveable member relative to the mounting plate, wherein the centrifugal force acting upon the protection member acts against a biasing force of the spring; a first stop extending from the mounting plate; a second stop extending from the mounting plate, wherein the bore is positioned substantially between the first stop and the second stop, wherein the second stop is configured to contact the moveable member to align the moveable member relative to the bore when the moveable member at least partially covers the bore, and wherein the moveable member is spaced from the first stop when in contact with the second stop.