ELECTROMAGNETIC CLUTCH

Abstract: An electromagnetic clutch includes a first rotatable member (30) rotatably supported on a first bearing. The first rotatable member (30) is provided with at least one annular groove along an outer surface thereof for receiving a belt (210) rotatably connecting the first rotatable member (30) to an external driving source. The first rotatable member (30) further has an inner and outer cylindrical annular portion (32, 31) and a magnetic axial end plate (33) connecting the cylindrical annular portions at an axial one end. The magnetic axial end plate (33) has a plurality of arcuate slits (301, 302) disposed on at least one circle. A plurality of remaining regions are located between each pair of adjacent slits. A second rotatable member (20) is rotatably supported on a second bearing. An annular magnetic member (50) is supported on the second rotatable member so as to be capable of limited axial movement. The annular magnetic member (50) faces the axial end plate (33) of the first rotatable member (30) with an axial gap therebetween. An electromagnet (70) is associated with the first rotatable member (30) and the annular magnetic member for attracting the other rota­ table member and the annular magnetic member. The remaining regions are mechanically reinforced by increasing the thickness thereof.

Description: This invention generally relates to an electromagnetic clutch, and more particularly, to a mechanically reinforced rotor which can cope with increased tension in the driving belt. Electromagnetic clutches are well known in the prior art and are often used for controlling the transfer of power from an automobile engine to the refrigerant compressor of an automobile air conditioning system. One such electromagnetic clutch (corresponding to the preamble of Claim 1) is disclosed in Japanese Utility Model Application Publication No. 63-42936 which corresponds to U.S. Patent No. 4,892,176. The construction of an electromagnetic clutch disclosed in the '936 Japanese Utility Model is shown in Figure 1. With reference to Figure 1, the clutch assembly is disposed on the outer peripheral portion of annular tubular extension 11, which projects from an end surface of compressor housing 10 to surround drive shaft 20. Drive shaft 20 is rotatably supported in compressor housing 10 by a bearing (not shown). The clutch assembly includes rotor 30 rotatably mounted on tubular extension 11 by bearing 12. Rotor 30 is coupled to the autombile engine (not shown) through a belt (not shown). Rotor 30 has a U-shaped configuration in its sectional side view, and includes outer cylindrical portion 31, inner cylindrical portion 32, and axial end plate portion 33. End plate portion 33 connects the outer and inner cylindrical portions 31 and 32 at one axial end. Axial end plate portion 33 is provided with a plurality of concentric arcuate slits 301, 302, which are disposed on outer and inner concentric circles, respectively. Slits 301, 302 are angularly synchronized and oriented of equiangular intervals as shown in Figure 3. This construction forms magnetic pole face 303. Hub 40 is fixed to the outer terminal end of drive shaft 20 extending beyond tubular extension 11. Armature plate 50 is movably connected to hub 40 by a plurality of leaf springs 60. As discussed below, leaf springs 60 permit axial movement of armature plate 50 toward pole face 303. Leaf springs 60 are fixed to the outer surface of armature plate 50 by rivets 51. The axial end surface of armature plate 50 faces pole face 303 of rotor 30 with a predetermined axial air gap "G" therebetween. The axial end surface of armature plate 50 is provided with concentric arcuate slits 501, forming pole face 502. Slits 501 are positioned to be opposite the midway point between slits 301, 302 on pole face 303. Electromagnet 70 is mounted on compressor housing 10 concentric with drive shaft 20. Electromagnet 70, including the electromagnetic coil 71 provided therewithin, is disposed within annular hollow portion 304 of rotor 30 such that is surrounded by an air gap. When coil 71 of electromagnet 70 is energized, pole face 502 is attracted to pole face 303. Thus, drive shaft 20 rotates as rotor 30 is turned by the engine. If coil 71 of electromagnet 70 is not energized, pole face 502 of armature plate 50 is separated from pole face 303 of rotor 30 by the recoil strength of leaf springs 60. Rotor 30 still rotates in response to the engine output, but drive shaft 20 is not turned. In the above construction of the electromagnetic clutch, magnetic flux "M", which is produced around electromagnetic 70 by the energizing of electromagnetic coil 71, passes through a magnetic passageway formed within electromagnet 70, rotor 30 and armature plate 50 as indicated by the dotted line in Figure 1. In recent years, in order to effectively utilize the restricted vacant space in an automobile engine compartment, the respective pulleys or rotors associated with the automobile engine and devices deriving power from the engine (such as an automobile generator, an oil hydraulic pump used for a power assisted steering wheel, and the refrigerant compressor) receive only one driving belt as shown in Figure 2. With reference to Figure 2, pulleys 300, 400, and 500 are associated with the automobile engine, the automobile generator and the oil hydraulic pump, respectively. Rotor 30 is one of the rotatable members of the electromagnetic clutch which is associated with the refrigerant compressor. Pulley 600 is a so-called "idle pulley", which is used for adjusting the tension in driving belt 200. Driving belt 200 is sequentially received by pulley 300, pulley 400, rotor 30, pulley 500, and pulley 600. When driving belt 200 is received by pulleys 300, 400, 500 and 600 and rotor 30, the tension of driving belt 200 is adjusted to an increased level to avoid a reduction in the capacity of transferring the driving power from the automobile engine to the automobile generator, the oil hydraulic pump and the refrigerant compressor. Specifically, an increased tension in the driving belt generates a force which seriously tends to nutate rotor 30. As a result of the rotor's U-shaped configuration undesirable metal fatigue occurs at a certain circumferential portion "F" of axial end plate portion 33 of rotor 30. The circumferential portion F lies adjacent the inner circular arc of slits 302 disposed on the inner concentric circle. As can be appreciated, such fatigue causes serious damage to rotor 30. In order to resolve this drawback, rotor 30 must be mechanically reinforced. However, when rotor 30 is mechanically reinforced by increasing the thickness of axial end plate portion 33, the increased weight of rotor 30 will be above a negligible amount. In addition, an increase in the thickness of axial end plate portion 33 makes the blanking process for forming slits 301 and 302 more difficult. Furthermore, when rotor 30 is mechanically reinforced by increasing the arcuate distance of each remaining region 301a, 302a located between adjacent arcuate ends of slits 301, 302, a resulting decrease of magnetic attraction force acting between pole faces 502 and 303 will be above a negligible amount. Accordingly, it is an object of this invention to provide an electromagnetic clutch having a mechanically reinforced rotor which can cope with increased tension in a driving belt without a corresponding increase in its own weight. It is another object of this invention to provide an electromagnetic clutch having a mechanically reinforced rotor which can cope with increased tension in a driving belt without a corresponding decrease of magnetic attraction force acting between the armature plate and the rotor. An electromagnetic clutch according to the present invention includes a first rotatable member, a second rotatable member, and an annular armature plate. The armature plate is composed of magnetic material and is connected to the second rotatable member so that the annular armature plate is capable of limited axial movement. The first rotatable member comprises a first cylindrical annular portion, a second cylindrical annular portion concentrically disposed within the first annular portion, and an annular end plate composed of magnetic material and connecting one axial end of each of the first and second cylindrical annular portions. The first and second cylindrical annular portions and the annular end plate collectively define an annular cavity. The annular end plate further defines a plurality of arcuate slits which are disposed on a first and second circles concentrically positioned with said cylindrical annular portions. A plurality of remaining regions are located between each pair of adjacent arcuate ends of the slits disposed on each circle. The armature plate faces the annular end plate of the first rotatable member such that an axial air gap is defined therebetween. An electromagnet is disposed within the annular cavity to attract the armature plate into contact with the annular end plate such that rotation of the first rotatable member can be transmitted to the second rotatable member through the armature plate when said electromagnet is activated, wherein said remaining regions of said annular end plate comprise reinforcing members being thicker than the other portions of the annular end plate. Figure 1 is a vertical cross-sectional view of a prior art electromagnetic clutch. Figure 2 is a schematic arrangement plan of pulleys or rotors which are associated with the driving source and the driven devices driven by the driving source, respectively. Figure 3 is a cross-sectional view of a rotor taken along line 3-3 of Figure 1. Figure 4 is a vertical cross-sectional view of an electromagnetic clutch in accordance with a first embodiment of the present invention. Figure 5 is a cross-sectional view of the rotor taken along line 5-5 of Figure 4. Figure 8 is a vertical cross-sectional view of the rotor of the electromagnetic clutch in accordance with a modified embodiment of the present invention. Figure 7 is a view similar to Figure 5 showing the rotor of the electromagnetic clutch in accordance with an embodiment of the present invention. Figure 8 is a cross-sectional view taken along line 8-8 of Figure 7. Figure 9 is a view similar to Figure 8 showing the rotor of the electromagnetic clutch in accordance with a modified embodiment of the present invention. The construction of an electromagnetic clutch in accordance with a first embodiment of this invention is shown in Figure 4. In the drawing, the same numerals are used to denote the corresponding elements shown in Figure 1. Further elements shown in Figure 4 are as described below. An opening 101 is formed at the center of the end surface of compressor housing 10. A needle bearing 21 is disposed in an annular peripheral wall of opening 101 for rotatably supporting drive shaft 20. Annular member 72 is disposed around annular tubular extension 11 and is used for firmly attaching electromagnet 70 to the end surface of compressor housing 10. Shaft seal assembly 22 is disposed in cavity 23 defined by annular tubular extension 11. Stopper plate 41, fixed at an outer end of drive shaft 20 by nut 42, supports armature plate 50 through a plurality of leaf springs 60. An outer peripheral surface of outer cylindrical portion 31 of rotor 30 receives flat belt 210 which couples rotor 30 to a rotatable member of a driving source, for example, a drive shaft (not shown) of the automobile engine. Flat belt 210 is provided with a plurality of U-shaped grooves 211 formed along its inner peripheral surface. Outer cylindrical portion 31 of rotor 30 is also provided with a plurality of U-shaped grooves 311 formed along its outer peripheral surface so as to firmly receive U-shaped grooves 211 of flat belt 210. In general, flat belts are more useful and durable than V-shaped belts when they are sequentially received by a plurality of pulleys. With additional reference to Figure 5, rotor 30 is provided with a plurality of rectangular parallelepiped members 330 for mechanical reinforcement. The parallelepiped members 330 are integrated with rotor 30 and oriented such that each radially extends from inner cylindrical portion 32 to outer cylindrical portion 31 along remaining regions 302a and 301a. The ends of the rectangular parallelepiped members 330 are spaced apart from electromagnet 70 so that the axial air gap remains therebetween. Hence, with this construction, undesirable metal fatigue of rotor 30 is sufficiently prevented when flat belt 210 is used under high tension. Moreover, the enhanced resistance of rotor 30 is achieved without virtually any increase in the rotor's weight or decrease of magnetic attraction force acting between pole faces 502 and 303. Figure 6 illustrates a first modified embodiment of this invention. With reference to Figure 6, rotor 30 is provided with a plurality of wedge-shaped members 331. Each wedge-shaped member 331 radially extends along a remaining region 302a from inner cylindrical portion 32 to approximately two-thirds of the way across axial end plate 33. Additionally, each wedge-shaped member tapers toward outer cylindrical portion 31. The tapered end of each wedge-shaped member 331 is adjacent to an inner circular arc of slit 301. Figures 7 and 8 illustrate a second modified embodiment of this invention. With reference to Figures 7 and 8, remaining regions 301a and 302a are angularly shifted relative to each other. Rotor 30 is provided with a plurality of wedge-shaped members 332. Each wedge-shaped member 332 radially extends along a remaining region 302a from inner cylindrical portion 32 to approximately two-thirds of the way across axial end plate 33. Additionally, each wedge-shaped member 332 tapers toward outer cylindrical portion 31. The tapered end of each wedge-shaped member 332 is adjacent to the inner circular arc of slit 301. Figure 9 illustrates a further modified embodiment of this invention. With reference to Figure 9, rotor 30 is provided with a plurality of rectangular parallelepiped members 333. Each parallelepiped member 333 radially extends from inner cylindrical portion 32 to approximately two-thirds of the way across axial end plate 33 along a remaining region 302a. The outer radial ends of parallelepiped members 333 are adjacent to the inner circular arc of slit 301. The effect of the above three embodiments is similar to the effect of the first embodiment. Therefore, description of the effect of the above three embodiments is omitted.

Claims: Electromagnetic clutch including a first rotatable member (30), a second rotatable member (20), an annular armature plate (50) of magnetic material connected to said second rotatable member (20) so that said annular armature plate (50) is capable of limited axial movement, and an electromagnet (70), said first rotatable member (30) comprising a first cylindrical annular portion (31), a second cylindrical annular portion (32) concentrically disposed within said first cylindrical annular portion (31) and an annular end plate (33) of magnetic material connecting one axial end of each of said first and second cylindrical annular portions (31, 32), said first and second cylindrical annular portions and said annular end plate defining an annular cavity, said annular end plate (33) being provided with a plurality of arcuate slits (301, 302) which are disposed on at least one circle concentric with said cylindrical annular portions (31, 32) and a plurality of remaining regions (301a, 302a) located between adjacent ends of said arcuate slits (301, 302), said annular armature plate (50) facing said annular end plate (33) of said first rotatable member (30) with an axial air gap therebetween, said electromagnet (70) being disposed within said annular cavity and operable to attract said annular armature plate (50) into contact with said annular end plate (33) such that the rotation of said first rotatable member (30) can be transmitted to said second rotatable member (20) through said annular armature plate (50) when said electromagnet is activated, characterised in that said remaining regions (301a, 302a) of said annular end plate (33) comprise reinforcing members (330, 331, 332, 333) being thicker than the other portions of said annular end plate (33). Electromagnetic clutch according to claim 1, wherein said annular end plate (33) defines a plurality of arcuate slits (301, 302), characterized in that said arcuate slits are disposed on first and second circles concentric with said cylindrical annular portions (31, 32), a diameter of said first circle being greater than a diameter of said second circle, a plurality of first remaining regions (301a) being located between adjacent ends of said arcuate slits (301) disposed on said first circle, and a plurality of second remaining regions (302a) being located between adjacent ends of said arcuate slits (302) disposed on said second circle, at least said second remaining regions (302a) comprising reinforcing members (332) being thicker than the other portions of said annular end plate (33). The electromagnetic clutch of claim 2, wherein said first rotatable member (30) is provided with a plurality of reinforcing members (332) projecting from one end surface of said second remaining regions (302a) opposite to said annular armature plate (50), respectively. The electromagnetic clutch of claim 3, wherein each said reinforcing members (332) extends from an outer peripheral surface of said second cylindrical annular portion (32) to a portion adjacent to an inner circular arc of one of said slits (301) disposed on said first circle. The electromagnetic clutch of one of claims 2 to 4, wherein said arcuate slits (301, 302) are disposed on said first and second circles at equiangular intervals. The electromagnetic clutch of one of claims 2 to 5, wherein said arcuate slits (301) disposed on said first circle are angularly synchronized with said arcuate slits (302) disposed on said second circle. The electromagnetic clutch of claim 6, wherein said first rotatable member (30) is provided with a plurality of reinforcing members (330), projecting from one end surface along said first and second remaining regions (301a, 302a) opposite to said annular armature plate (50). The electromagnetic clutch of one of claims 1 to 7, wherein each said reinforcing member (330, 331, 332, 333) is a rectangular parallelopiped. The electromagnetic clutch of one of claims 1 to 8, wherein each said reinforcing member (330, 331, 332, 333) extends from an outer peripheral surface of said second cylindrical annular portion (32) to an inner peripheral surface of said first cylindrical annular portion (31). The electromagnetic clutch of one of claims 2 to 7 or 9, wherein each said reinforcing member (331, 332) is wedge shaped, and preferrably wherein each said projection is tapered towards said first cylindrical annular portion. The electromagnetic clutch of one of claims 5 to 10, wherein said arcuate slits (301) disposed on said first circle are angularly shifted with respect to said arcuate slits (302) disposed on said second circle. The electromagnetic clutch of one of claims 2 to 11, wherein said annular end plate (33) defines said slits (301, 302) on a plurality of concentric circles and wherein each said reinforcing member (332, 333) extends from said inner cylindrical portion (32) to a point beyond at least one of said concentric circles but short of at least one of said concentric circles.

Inventors: SHIMURA, KEIICHI
Applicants: SANDEN CORPORATION
Application year: 1990
Main classification: F16D27
IPC codes: G06K7, F16D27