GB2039334A - Counterbalanced electromagnetic band clutch - Google Patents

Abstract

In an electromagnetically operated band clutch (10) comprising a band (52) arranged in a radial gap 50 between driving and driven members (12), (36) and including an electromagnetic coil (32) carried by the driving member (12) to urge the band into driving engagement with the driving member when the clutch is engaged, in order to overcome the centrifugal forces and thereby increase the maximum speed of the engaged clutch, a lever (62) (Figure 2, not shown) is pivotally connected (64) to the driven member. One end (66) of the lever is adapted to engage the band, and the opposite end (68) of the lever carries a weight (70). Rotation of the clutch forces the weight radially outwardly with respect to the clutch, thereby pivoting the lever to force the opposite end of the lever into engagement with the band, to maintain the band back into engagement with the driving member. <IMAGE>

Description

SPECIFICATION Counterbalanced electromagnetic band clutch The invention relates to a counterbalanced electromagnetic band clutch.

It has already been disclosed an engine fan electromagnetic band clutch in which a metal band circumscribes a driving member, and is engaged therewith by a magnetic coil which pulls the band into driving engagement with the driving member when the clutch is engaged. Of course, in this type of clutch, at some predetermined maximum speed, centrifugal forces tending to urge the band outwardly away from the driving member will overcome the electromagnetic force which holds the band into engagement with the driving member. Accordingly, at his predetermined maximum speed, the clutch will automatically disengage.

It is an objet of the present invention to provide a counter balanced electromagnetic band clutch in which the maximum engaged speed is substantially higherthan the maximum engaged speed of clutches known to the prior art.

To this end the invention proposes a counterbalances electro-magnetic banc clutch including a pair of coaxial relatively rotatable members comprising a driving member and a driven member, said members having corresponding radial offset portions defining a yap therebetween, a circumferentially extending band located in said gap, means drivingly engaging said band with one of said members when the clutch is engaged, the other member defining a circumferential surface facing said band, electromagnetic means for forcing said band into driving engagement with said circumferential surface when the clutch is engaged, characterized in that it further comprises counterbalancing means effective only upon engagement of the clutch for exerting a force on said band and maintaining said band engaged with said circumferential surface.

The invention will now be described with reference to the accompanying drawing wherein: Figure l is an axial cross-sectional view of a clutch according to the present invention ; and Figure 2 is a fragmentary cross-sectional view taken substantially along lines 2-2 of Figure 1.

Referring now to the drawing, a clutch and fan assembly generally indicated by the numeral 10 includes a driving member 12 which terminates in a flange 14 for connection with the vehicle engine (not shown), so that the driving member 12 is rotated by operation of the engine. The other end of the driving member 12 carries a slip ring assembly generally indicated by the numeral 15. The slip ring assembly includes a member 16 B which is fixed for rotation with the driving member 12 and a slip member 18 which is mounted so that the member 16 can rotate relative to the member 18. Connecting wires 20, 22 extend from the members 18 and 16 respectively, so that an electrical connection is provided between the connecting wires 20 and 22 by the members 16 and 18 of the slip ring assembly 15.The connecting wire 20 is connected to appropriate vehicle engine temperature and/or air conditioning pressure sensors of a type well-known to those skilled in the art. Since these sensors are conventional ,they will not be described in detail herein. The connecting wire 22 is carried within passage 23 in the driving member 12.

The driving member 12 also carries a circumferentially extending spool or bracket 24 which is made of magnetic material and which is mounted for rotation with the driving member 12. The spool or bracket 24 includes a pair of axially spaced, circumferentially extending pole piece portions 26,28 which circumscribe the driving member 12 and which cooperate with another two define a cavity 30 therebetween. An electromagnetic coil comprises windings 32 disposed in the cavity 30 and are wrapped circumferentially around the driving member 12. The windings 32 are connected with the connecting wire 22, so that when an electrical signal is transmitted through the connecting wire 20, electrical current will be transmitted to the coil 32 by the connecting wire 20, the slip ring 15, and the connecting wire 22.

A bearing 34 mounted on the driving member 12 between the spool or bracket 24 and the slip ring assembly 15, mounts a driven member 36 for rotation relative to the driving member 12. Bolts 38 attach fan blades 40 to the driven member 36, so that the fan blades 40 are rotated with the driven member 36. Of course, it will be understood by those skilled in the art that additional fan blades 40 are spaced circumferentially around the periphery of the driven member 36 in a manner well-known to those skilled in the art. The driven member 36 further includes an axially extending portion 42 which projects from the driven member 36 and which circumscribes the pole piece portions 26 and 28 of the spool or bracket 24.

The inner circumferential surface 44 of the portion 42 cooperates with the outer circumferential edges 46, 48 of the pole piece portions 26 and 28 to define a gap 50 therebetween. A circumferentially extending band 52 is disposed in the gap 50. One end of the band 52 is connected to the axially extending portion 42 of driven member 36 by connecting mechanism 54. The band 50 extends from the portion 54 in a direction such that the band wraps around the driving member 12 in the direction in which the latter rotates. Of course, driving member 12 is able to rotate in a single direction only, since it is operated directly by the vehicle engine.

The band is made from magnetic material, as are the pole piece portions 26, 28, so that a magnetic circuit is defined consisting of pole piece portions 26, 28 and the band 50. The outer peripheral portions 56, 58 of the radially inner edge of the band 52 are adapted to frictionally engage the outer circumferential edges 46,48 of the pole piece portions 26,28 when the clutch is engaged. Accordingly, it will be noted that the band 52 bridges the cavity 30 in which the magnetic coil consisting of windings 32 is housed.

Clearly, at some predetermined maximum engaged speed, centrifugal forces urging the band 52 radially outwardly with respect to the members 12, 36 will overcome the electromagnetic force holding the band 52 in engagement with driving member 12.

When this occurs, of course, the clutch automatically disengages. In order to increase this maximum engaged speed, a counterbalance mechanism generally indicated by the numeral 60 has been provided. A portion of the driven member 36 is cut away to define a slot as at 61. The counterbalance mechanism 60 includes a lever 62 which is connected to the driven member 36 by a pivot pin 64 which is located intermediate the opposite ends 66, 68 of the lever 62. The pin 64, of course, is also secured to the outer circumferential surface of the drive member 36 by any conventional mechanism. A weight 70 is attached to the end 68 of the lever 62. As most clearly seen in Figure 2, the end 66 of lever 62 is able to engage the end 72 of the band 52 when the lever 62 pivots in the counterclockwise direction about the pivot 64.End 72 of band 52 is the end of the band 52 opposite the end thereof which is secured to the driven member 36 by the connecting mechanism 54.

The various components of the clutch mechanism 10 are illustrated in the drawings in the position they assume when the clutch is disengaged. In this condition, the driving member 12, of course, will be rotated by the vehicle engine, but the driven member 36 will not be driven thereby, because there is no driving connection between the driving member 12 and the driven member 36. Of course, in this condition, the bearing 34 permits the driving member 12 to rotate without driving the driven member 36. When the aforementioned temperature and pressure sensors (not shown) sense an engine operating condition in which operation of the engine cooling fan is required, en electrical signal is transmitted through the connecting wire 20 and 22 to energize the coil comprising the windings 32.When this occurs, magnetic flux created in the magnetic circuit defined by the pole piece portions 26, 28 and the inner band member 54 causes the latter to move radially, viewing Figure 1, in a direction toward the pole pieces 26, 28. Consequently, the outer peripheral portions 58,60 of the inner edge of the inner band member 52 will be brought into engagement with the outer circumferential edges 46,48 of the pole piece portions 26, 28, thereby maintaining the clutch in engagement to cause the driving member 12 to rotate the driven member 36, to provide a driving connection causing the fan blades 40 to rotate with the driving member 12.When the clutch is to be disengaged, current to the windings 32 is turned off, permitting the band 52 to separate from the pole piece portions 26, 28, thereby breaking the driving connection between the driving member 12 and the driven member 36.

As discussed hereinabove, at some maximum engagement speed, centrifugal forces acting on the band 52 and tending to urge the latter radially outwardly with respect to the driving member 12 overcome the predetermined electromagnetic force generated by the coil which holds the band 52 against the driving member 12. In order to increase the maximum engaged speed of the fan and to overcome the centrifugal forces, the counterbalance mechanism 60 has been provided. When the clutch is disengaged, of course, the driven member 36 merely freewheels on the bearing 34. Accordingly, when the clutch is disengaged, there will be very little force acting on the weight 70 carried by the lever 62.However, upon engagement of the clutch, when the driven member 36 begins rotating with appreciable speed, centrifugal forces generated by rotation of the members 12 and 36 acting on the weigth 70 tend to urge the latter radially outwardly viewing Figure 2. When this occurs, the lever 62 pivots about the pivot 64 so that the end 68 and weight 70 move radially outwardly viewing Figure 2.

As the lever pivots, the end 66 of the lever will be forced radially inwardly viewing Figure 2, thereby engaging the end 72 of the band 52, to hold the band against the driving member 12 with a force proportional to the speed of rotation of the driven member 36. Accordingly, the centrifugal forces tending to urge the band 52 away from the driving member 12 are overcome by an equivalent force generated by the counterbalance mechanism 60 which acts on the band 52 in opposition to the centrifugal forces, so that the maximum engaged speed is significantly increased.

Claims (11)

1. A counterbalanced electromagnetic band clutch including a pair of coaxial relatively rotatable members comprising a driving member (12) and a driven member (36), said members having corresponding radial offset portions defining a gap (50) therebetween, a circumferentially extending band (52) located in said gap, means (54) drivingly engaging said band with one of said members when the clutch is engaged, the other member defining a circumferential surface (46,48) facing said band, electromagnetic means (30) for forcing said band into driving engagement with said circumferential surface when the clutch is engaged, characterized in that it further comprises counterbalancing means effective only upon engagement of the clutch for exerting a force on said band and maintaining said band engaged with said circumferential surface.

2. A counterbalanced electromagnetic band clutch according to claim 1, characterized in that said counterbalancing means (60) includes means (62, 70) for regulating said force exerted on the band (52) as a function of the speed of rotation of said driven member (12).

3. A counterbalanced electromagnetic band clutch according to claim 2, characterized in that said other member is located so that centrifugal forces generated by rotation of said members urges said band away from said circumferential surface, and said counterbalance means opposes said centrifugal forces.

4. A counterbalanced electromagnetic band clutch according to claim 3, characterized in that said band (52) has a pair of ends, said drivingly engaging means (54) being secured to one end of said band, and said counterbalance means (60) engaging the opposite end (72) of said band (52).

5. A counterbalanced electromagnetic band clutch according to claim 3, characterized in that said counterbalance means (60) includes a weighted member (62) responsive to rotation of said driving (12) and driven (36) members to oppose movement of the band (52) away from said circumferential surface.

6. A counterbalanced electromagnetic band clutch according to claim 5, characterized in that said weighted member includes a lever (62) pivotally mounted (64) on said one member, said lever having one end (66) adjacent said band (52) and an opposite end (68) to which a weight (70) is secured.

7. A counterbalanced electromagnetic band clutch according to claim 6, characterized in that said band (52) has a pair of ends, said drivingly engaging means (54) being secured to one end of said band, said one end (66) of said lever (62) being adapted to engage the other end (72) of the band.

8. A counterbalanced electromagnetic band clutch according to claim 1, characterized in that said counterbalancing means (60) includes a weighted member (62), said weighted member being respon size to rotation of said driving and drivem members to oppose movement of the band away from said circumferential surface.

9. A counterbalanced electromagnetic band clutch according to claim 1, characterized in that said counterbalancing means includes a lever (62) pivotally mounted (64) on said one member, said lever having one end thereof (66) adjacent said band (52) for engaging the latter to maintain the band in engagement with the circumferential surface when the clutch is engaged.

10. Acounterbalanced electromagnetic band clutch according to claim 9, characterized in that said lever has an opposite end (68), a pivot (64) located between the ends of the lever mounting the lever on said one member, and a weight (70) secured to said opposite end of the lever.

11. An electromagnetic band clutch substantially as described and as shown in the accompanying drawing.