GB2156013A - Electromagnetic clutch - Google Patents

Abstract

A tubular magnetic reinforcement ring 10 is provided which decreases the magnetic resistance to the flow of magnetic flux. The tubular member 10 is positioned so that flux flow 29 is divided into two paths. Accordingly, high magnetic attraction force is produced which enables a high level of torque transfer when armature plate 8 is magnetically attracted to pulley 14 by the flux generated by a coil 4. The plate 8 frictionally engages the pulley against the pressure of leaf-springs 7 and transmits drive to a shaft 5. <IMAGE>

Description

SPECIFICATION Improved electromagnetic clutch The present invention relates generally to the field of electromagnetic clutches, and more particularly, is directed to an improved electric magnetic clutch which can transfer a high level of torque between a prime mover and a driven apparatus.

It is an overall object of the present invention to provide an electromagnetic cluthc which can transfer a high level of torque between a prime mover and a driven apparatus.

It is another object of the present invention to provide an electromagnetic clutch which is simpler in construction and more easy to manufacture than such clutches known in the prior art.

These and other objects of the present invention are achieved by providing a tubular magnetic reinforcement ring which is positioned adjacent the outer race used to hold the bearing rotatably supporting the pulley of the electromagnetic clutch. The reinforcement ring reduces the resistance to the flow of magnetic flux associated with the inner portion of the housing containing the electric coil.

Thus more attractive force is produced, enabling the electromagnetic clutch to transfer a higher level of torque.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical cross-sectional view of a conventional electromagnetic clutch.

Figure 2 is a vertical cross-sectional view of an electromagnetic clutch in accordance with the present invention.

With reference to Fig. 1, a conventional electromagnetic clutch is shown assembled on a compressor for an automobile air conditioning system. The compressor includes a housing 1' which is provided with tubular extension 1 a' surrounding drive shaft 5' of the compressor. Drive shaft 5' is rotatably supported in compressor housing 1' by bearings.

A pulley 14' having an axial end plate 3' is rotatably supported on tubular extension 1a' by radial bearing 2'. Radial bearing 2' is mounted on the outer peripheral surface of tubular extension 1 a'. An electromagnetic device 16', comprising magnetic coil 4' enclosed in coil housing 12', is disposed on tubular extension 1 a' and fixed to compressor housing 1'. Coil housing 12' includes outer portion 1 2a', rear portion 1 2b' and inner portion 1 2c'. A hub 6' is disposed on an outer terminal end of drive sahft 5' and is attached thereto by bolt 18'. Hub 6' is coupled to armature plate 8' through a plurality of leaf-springs 7'. Armature plate 8' is positioned immediately adjacent axial end plate 3' of pulley 14' with an air gap therebetween.

Pulley 14' comprises outer cylindrical member 141' which has a V-shaped groove 141a' for receiving a V-belt in engagement with the engine of an automobile. As pointed out above, pulley 14' also includes axial end plate 3'. End plate 3' extends radially inwardly from an end portion of cylindrical member 141'. Pulley 14' further includes an annular shaped member 143' made of a magnetic material which is attached to end plae 3' inwardly of the inner peripheral surface of outer cylindrical member 141' and adjacent the outer surface of outer race 2a' which holds bearing 2' for rotatably supporting pulley 14'.

When coil 4' of electromagnetic device 16' is energized, magnetic flux is produced and flows as indicated by arrows 29' around a closed loop as shown in Fig. 1. The magnetic flux passes through outer cylindrical member 141' of pulley 14', coil housing 12', annular shaped member 143', portions of armature plate 8' and end plate 3' and back to outer cylindrical member 141'.

Armature plate 8' is, therefore, magnetically attracted to pulley 14' by the above mentioned flow of magnetic flux and moves toward pulley 14' against the strength of leafsprings 7'. Thus, armature plate 8' is brought into frictional engagement with end plate 3' of pulley 14' and rotates together with pulley 14'. Therefore, the rotating motion of the automotive engine is transmitted to drive shaft 5' of the compressor through pulley 14', armature plate 8', leaf-springs 7' and hub 6'.

When coil 4' of electromagnetic device 16' is de-energized, magnetic flux is no longer produced. Thus, armature plate 8' is separated from end plate 3' of pulley 14' and is returned to a resting position by the bias strength of leaf-springs 7'.

As shown in Fig. 1, pulley 14' extends over coil housing 12' of electromagnetic device 16', with air gap 16a' between outer cylindrical member 141' and outer portion 12a' and air gap 16b' between annular shaped member 143' and inner portion 12c'. Thus, when coil 4' is energized, the magnetic flux must flow through gaps 16a' and 16b'.

Outer portion 12a' and inner portion 12c' of housing 12' form respective cylinder surfaces. Because the diameter of the cylinder formed by portion 12a' is larger than the diameter of the cylinder formed by portion 12c'; the resistance to the flow of magnetic flux across gap 16a' is smaller than the resistance to the flow of magnetic flux across gap 16b'. This is so because the circumferential surface area of outer portion 12a' is larger than the circumferential surface area of inner portion 12c' and magnetic resistance is inversely proportional to surface area. Thus, the magnetic flux indicated by arrows 29' in Fig.

1 flows through gap 16a' relatively easily due to the low magnetic resistance of outer por tion 12a'. However, the flow of magnetic flux is impeded across gap 16b' due to the high magnetic resistance of inner portion 12c'. As a result, the amount of magnetic flux flowing through the closed loop is limited. Thus, the amount of attractive force drawing armature plate 8' into engagement with end plate 3' is also limited. Accordingly, the electromagnetic clutches of the type shown in Fig. 1 cannot be used to transfer large amounts of torque from a prime mover to a driven apparatus.

The above mentioned deficiency can be overcome somewhat by extending inner portion 1 2c' outwardly toward end plate 3'. This approach is limited, however, by the presence of V-shaped groove 141 a' which is necessarily small in diameter in order to maintain the overall size of the electromagnetic clutch small. Thus, inner portion 12c' cannot be extended without interfering with V-shaped groove 141razz Accordingly, the amount of magnetic flux flow, and thus torque transfer level of the clutch, cannot be increased.

With reference to Fig. 2, an electromagnetic clutch in accordance with the present invention is shown assembled on a compressor for an automobile air conditioning system. A compressor is merely one example of an apparatus which can be effectively coupled to a prime mover by the present invention and the invention is, of course, not limited thereto. The compressor includes a housing 1 which is provided with cantilevered tubular extension 1 a surrounding drive shaft 5 of the compressor. Drive shaft 5 is rotatably supported in compressor housing 1 by bearings.

A pulley 14, having an axial end plate 3, is rotatably supported on tubular extension 1 a by radial bearing 2 which is mounted on the outer peripheral surface of tubular extension 1 a. An electromagnetic device 1 6 comprising magnetic coil 4 enclosed in coil housing 1 2 is disposed on tubular extension 1 a and fixed to compressor housing 1. Coil housing 1 2 includes outer portion 12a, rear portion 1 2b and inner portion 12c. Hub 6 is disposed on an outer terminal end of drive shaft 5 and is attached thereto by bolt 18. Hub 6 is coupled to armature plate 8 through a plurality of leafsprings 7. Armature plate 8 is positioned immediately adjacent end plate 3 of pulley 14 with an air gap therebetween.

Pulley 14 comprises outer cylindrical member 141 which has a V-shaped groove 141a for receiving a V-belt in engagement with the engine of an automobile. As mentioned above, pulley 14 also includes axial end plate 3 extending radially inwardly from an end portion of outer cylindrical member 141. An annular shaped member 1 43 made of a magnetic material is attached to end plate 3 inwardly of the inner peripheral surface of outer cylindrical member 141 adjacent the outer surface of outer race 2a holding bearing 2 for rotatably supporting pulley 1 4.

When coil 4 is energized, magnetic flux is produced and flows as indicated by arrows 29 around a closed loop as shown in Fig. 2. The magnetic flux passes through outer cylindrical member 141 of pulley 14 and portions 12a and 1 2b of housing 1 2. The flow of magnetic flux then separates into two paths as shown by arrows 29. One path passes through annular shaped member 143. The other path passes through cylindrical portion 1 5 of tubular extension 1 a, then through magnetic reinforcing ring 10 and outer race 2a holding bearing 2. The two paths merge and passes through portions of armature plate 8 and end plate 3 and then back to outer cylindrical member 141'.

Armature plate 8 is magnetically attracted to pulley 14 by the above mentioned magnetic flux generated by coil 4 and moves toward pulley 14 against the strength of leafsprings 7. Thus, armature plate 8 is brought into frictional engagement with pulley 1 4 and rotates together with pulley 14. Therefore, the rotating motion of the automotive engine is transmitted to drive shaft 5 of the compressor through pulley 14, armature plate 8, leafsprings 7 and hub 6.

When coil 4 is de-energized, magnetic flux is no longer produced. Thus, armature plate 8 is separated from axial end plate 3 of pulley 14 and is returned to a resting position by the bias strength of leaf-springs 7.

As can be seen in Fig. 2, pulley 14 encloses outer portion 1 2a and inner portion 12c of housing 1 2 around coil 4. Outer race 2a of radial bearing 2 is fitted inside a step portion 3b of annular shaped member 143 located inside pulley 14. Tubular magnetic reinforcement ring 10 is fitted adjacent annular shaped member 143, with the inner surface of the ring facing the outer surface of tubular extension 1 a with a gap therebetween.

Ring 10 is made of a high permeability material. One axial end of ring 10 is fixed against an axial end of outer race 2a. The other axial end of ring 10 is secured in position by calking at several points as indicated by reference number 3c.

Thus, outer race 2a of radial bearing 2 and magnetic reinforcement ring 10 are prevented from moving in an axial direction between step portion 3b and calking points 3c. Accordingly, it is unnecessary to use a snap ring to secure outer race 2a of radial bearing 2. Thus, a component part and assembly step are eliminated, thereby reducing manufacturing cost of the electromagnetic clutch.

In the magnetic clutch of the present invention, magnetic flux flows in two paths when coil 4 is energized. Thus, a greater attraction force is produced because reinforcement ring 10 reduces the resistance to the flow of magnetic flux associated with the inner portion of the housing containing the electric coil.

Accordingly, the electromagnetic clutch of the present invention may be used to transfer a higher level of torque.

The present invention has been described in detail in connection with a preferred embodiment. The embodiment, however, is merely an example and the invention is not restricted thereto. It will be understood by those skilled in the art from a reading of the specification that variations and modification can be made within the scope of the present invention as defined by the appended claims.

Claims (5)

1. An electromagnetic clutch including a first rotatable member having an axial end plate of magnetic material supported on the outer surface of a cylindrical projection extending from a fixed portion of said clutch through a radial bearing, a second rotatable member coaxially positioned with respect to said first rotatable member, an armature plate member coaxially positioned with respect to said first rotatable member and frictionally engageable therewith, and electromagnetic means associated with said axial end plate of said first rotatable member for attracting said second rotatable member to said axial end plate so that rotation of said first rotatable member is transmitted to said second rotatable member by operation of said electromagnetic means, wherein a tubular magnetic reinforcement ring is fitted in the inside diameter of said first rotatable member on the outer surface of said projection with a gap therebetween.

2. The electromagnetic clutch of claim 1, wherein said magnetic reinforcement ring is axially rigidly positioned immediately adjacent an outside portion of said radial bearing.

3. The electromagnetic clutch of claim 1, wherein said magnetic reinforcement ring is made of a high permability material.

4. The electromagnetic clutch of claim 1, wherein at least some of the magnetic flux produced by said electromagnetic mean flows through said magnetic reinforcement ring.

5. An electromagnetic clutch constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawinqs.