The present invention relates to an electromagnetic clutch and more particularly to an electromagnetic clutch suitable for intermittently transmitting power of an engine or motor of a vehicle to an in-vehicle driven device (for example, a compressor in an air conditioner for use in a vehicle).
As this type of electromagnetic clutches, for example, an electromagnetic clutch disclosed in Patent Document 1 has been known. The electromagnetic clutch disclosed in Patent Document 1 has an energization interrupting device configured to cut a cutting wire that forms a part of an electromagnetic coil to thereby forcibly interrupt electric power supply to the electromagnetic coil if a rotor temperature exceeds a predetermined temperature due to relative sliding between friction surfaces of a rotor and an armature. In this energization interrupting device, a thermally-actuated device is provided in the rotor and the cutting wire is provided in the electromagnetic coil unit. When the rotor temperature increases beyond the predetermined temperature, the thermally-actuated element is displaced by a predetermined distance toward the electromagnetic coil unit and then engaged with the cutting wire to cut the cutting wire.
Note that in the energization interrupting device provided with the thermally-actuated element and the cutting wire, the thermally-actuated element and the cutting wire should be positioned opposite to each other in a narrow space between the rotor and the electromagnetic coil unit. Thus, if it fails to precisely control a relative distance between the thermally-actuated element and the cutting wire in the axial direction of the electromagnetic clutch, or the direction in which the thermally-actuated element is displaced, the following problem occurs. That is, the energization interrupting device causes an operation error to unintentionally cut the cutting wire or fail to cut the wire. Since the thermally-actuated element is fixed to the rotor, its position in the axial direction of the electromagnetic clutch is defined at the design state according to the sizes of the rotor and bearing and the size of a housing of a driven device where the rotor is positioned and fixed. In addition, the displacement amount of the thermally-actuated element is determined in consideration of design factors such as materials and sizes. Regarding the position of the cutting wire in the axial direction of the electromagnetic clutch, the positional accuracy thereof varies depending on how the cutting wire is mounted to an end surface of the electromagnetic coil unit on the rotor side. If the cutting wire is not appropriately mounted, the position of the cutting wire varies largely in the axial direction of the electromagnetic clutch. As a result, the above operation error occurs and the reliability of the energization interrupting device lowers.
Regarding the energization interrupting device of the electromagnetic clutch disclosed in Patent Document 1, the document only remarks that winding end of an electromagnetic coil is engaged with a hook of a bobbin and used as a cutting wire. There is no description about the way to control the position of the cutting wire in the axial direction of the electromagnetic clutch.
The present invention has been made in view of the above problems and an object of the present invention is to provide an electromagnetic clutch that facilitates positional control of the cutting wire and enhances reliability of the energization interrupting device.
In order to achieve the above object, the present invention provides an electromagnetic clutch, including: a rotor unit provided with a rotor that is rotated with power of a driving source, and rotatably supported to a boss formed on an end surface of a housing of a driven device; an armature unit provided with an armature that is magnetically attracted to the rotor when the rotor is excited, and fixed to a rotation shaft of the driven device, which passes through the boss; an electromagnetic coil unit including: a bobbin having first and second flanges on both sides of a cylindrical portion with an electromagnetic coil wound around an outer circumference of the cylindrical portion positioned between the flanges, the coil serving to excite the rotor in response to electric power supply; and a ring case provided with a circular bobbin container and accommodated in a circular recess formed in the rotor, the ring case being fixed to the end surface of the housing of the driven device with an opening edge of the bobbin container facing toward the rotor; and a thermally-actuated element attached to the rotor unit, and displaced toward the electromagnetic coil unit at over a predetermined temperature, the thermally-actuated element serving to cut a cutting wire portion that forms a part of the electromagnetic coil to forcibly interrupt electric power supply to the electromagnetic coil, with the wire being placed toward the electromagnetic coil unit across a movement area of the thermally-actuated element. In the clutch, the bobbin includes: first and second wall portions extending opposite to each other from the first flange formed on the opening edge in the bobbin container toward a bottom wall in the circular recess of the rotor where the thermally-actuated element is mounted; an inner abutment portion extending from an extension end of the first wall portion toward an inner opening edge of the bobbin container; and an outer abutment portion extending from an extension end of the second wall portion toward an outer opening edge of the bobbin container. The bobbin is accommodated into the bobbin container such that the inner abutment portion and the outer abutment portion abut inner and outer opening edges of the bobbin, respectively. The cutting wire portion is stretched between both of the wall portions at a predetermined distance from an end surface of each of the first and second wall portions.
According to the electromagnetic clutch of the present invention, while the inner and outer abutment portions of the bobbin are engaged with an opening edge of the bobbin container of the ring case, the bobbin having the electromagnetic coil wound thereon is positioned and accommodated into the bobbin container. Thus, it is possible to define the position of the bobbin in the bobbin container in the axial direction of the electromagnetic clutch, and also to precisely position the cutting wire portion stretched between the first wall portion and the second wall portion, in the axial direction of the electromagnetic clutch. The reliability of the energization interrupting device can be enhanced as well.
An embodiment of the present invention will be described hereinafter with reference to the accompanying drawings.
In
The rotor unit 20 is rotated with power of an engine or motor, and provided with a rotor 21, a friction member 22, and a bearing 23.
The rotor 21 has a circular shape. The inner circumference thereof is rotatably supported to the outer circumference of a boss 1a as an end surface of a front housing 1 of the compressor by means of the bearing 23. On the outer circumference of the rotor 21, formed are grooves to which a belt for transmitting a rotational force from the engine or motor is hooked. More specifically, as shown in
The armature unit 30 transmits a power from an engine or motor to a compressor when an armature 33 is magnetically attracted to the rotor 21 in response to electric power supply to the electromagnetic coil 42. As shown in
The hub 31 is provided with a flange portion 31a and fixed to the tip end of a rotation shaft 2 of the compressor by means of a nut 5 (see
The electromagnetic coil unit 40 generates a magnetic attraction power by magnetizing the rotor 21. The unit includes a bobbin 41, the electromagnetic coil 42 wound around the bobbin, a ring case 43 having a circular recess that serves as a bobbin container for accommodating the bobbin 41, an annular disc-like fixing member 44 fixed to the ring case 43 and configured to form the other end surface of the electromagnetic coil unit 40, and a connecting portion 45 for connecting an external power supply in the vehicle and the electromagnetic coil 42.
As shown in
As shown in
The electromagnetic coil unit 40 is securely insulated by pouring a resin through the space between the ring case 43 and the bobbin 41 accommodated into the circular recess of the ring case 43. As shown in
When heat is generated due to relative sliding between the rotor 21 and the armature 31, the energization interrupting device 50 forcibly interrupts electric power supply to the electromagnetic coil 42. The energization interrupting device 50 is provided with thermally-actuated elements, for example, the bimetal 51 and the bridge wire 52 serving as a cutting wire portion that forms a part of the electromagnetic coil 42.
The bimetal 51 is formed in a substantially rectangular shape and accommodated in the circular groove 21g formed in the bottom wall 21c2 of the circular recess 21d in the rotor 21. One end thereof is fixed with a rivet 53, and the other end faces toward the rotation direction of the rotor 21. Note that the bimetal 51 could be fixed by any other fixing member such as a bolt. Since the bimetal 51 is accommodated and positioned in the circular groove 21g, when engaged with the bridge wire 52, the bimetal 51 can be prevented from tilting to the left or right relative to the rotation direction of the rotor 21 in response to the reaction force of the bridge wire 52. If sensing the temperature higher than a predetermined level, the bimetal 51 is displaced beyond a predetermined distance toward the electromagnetic coil unit 40. The bimetal 51 is preferably a snap action type that starts inverted motion at a predetermined temperature. The snap action type bimetal is hardly displaced at a temperature lower than an inverted motion temperature (temperature causing inverted motion) but is largely displaced at over the inverted motion temperature. By utilizing the inverted motion, the bridge wire 52 is cut. In general, in a compressor for an in-vehicle air conditioner, the electromagnetic clutch 10 could increase the temperature up to 150° C. Taking this temperature into account to set the inverted motion temperature for interrupting electric power supply to the electromagnetic coil 42, the temperature is appropriately set to 180° C. to 190° C.
The bridge wire 52 is obtained from the winding end (the ground side of the electromagnetic coil 42) of the electromagnetic coil 42 wound around the bobbin 41. The wire is stretched on one end surface of the electromagnetic coil unit 40 opposite to the bottom wall 21c2 in the circular recess 21d of the rotor 21 such that the wire crosses an area where the bimetal 51 moves along with the rotation of the rotor 21 (movement area of the bimetal 51) and also is engaged with the bimetal 51 displaced beyond a predetermined distance. More specifically, as shown in
As shown in
Here, a brief description is given of the general operation of intermittently transmitting power to the compressor by means of the electromagnetic clutch 10 and the operation of the energization interrupting device 50. If electric power is supplied to the electromagnetic coil 42 of the electromagnetic coil unit 40 under the condition that the rotor 21 is rotated with a rotational force from the engine, the rotor 21 is excited, and the generated electromagnetic force makes the armature 33 magnetically attracted to the rotor 21. Then, the armature 33 is rotated in sync with the rotor 21. The rotational force of the armature 22 is transmitted to the rotation shaft 2 of the compressor by way of the rubber unit 32 and the hub 31 to thereby operate the compressor. If the electric power supply to the electromagnetic coil 42 of the electromagnetic coil unit 40 is interrupted in this state, the rotor 21 is demagnetized, and the armature 33 is retracted from the rotor 21 due to a restoring force of the rubber 32c. No rotational force of the rotor 21 is transmitted to the armature 33. As a result, the rotation shaft 2 stops rotating and the compressor stops the operation. In the normal state, the temperature of the end surface portion 21c of the rotor 21 does not reach the predetermined temperature at which the bimetal 51 is displaced over the predetermined distance. As shown in
On the other hand, if an excessively larger torque than usual acts on the rotation shaft 2 due to, for example, damaged inner parts of the compressor, the contact surfaces of the rotor 21 and the armature 33 slide on each other to generate the friction heat, resulting in rapid temperature rise at the end surface portion 21c of the rotor 21. When the temperature of the end surface portion 21c increases rapidly, as shown in
According to the electromagnetic clutch 1 of this embodiment, the outer abutment portion 41g and the inner abutment portion 41f of the bobbin 41 abut against the end surface 43a1 of the outer cylindrical portion 43a of the ring case 43 and the end surface 43b1 of the inner cylindrical portion 43b, by which the bobbin 41 is positioned and accommodated in the circular recess of the ring case 43. The inner abutment portion 41f and the outer abutment portion 41g have the same height from the first flange surface 41b1 of the first flange 41b and also, the depth from the end surface of the outer wall 41e to the bottom of the first slit 41e1 is the same (depth h2) as that from the end surface of the inner wall 41d to the bottom of the second slit 41d1. Thus, the bridge wire 52 is stretched in parallel to the first flange surface 41b1 at a predetermined height from the first flange surface 41b1 of the first flange 41b. By precisely controlling the height h1 (see
Consider the possibility that, if the bimetal 51 is largely displaced, the displaced end portion of the bimetal 51 abuts the electromagnetic coil portion 47 that crosses over the first flange surface 41b1 of the first flange 41b of the bobbin 41 and the bimetal 51 is damaged thereby. In this embodiment, since the first flange surface 41b1 of the first flange 41b has the inclined surface 41b3, the displaced end portion is guided along the inclined surface 41b3 and thus goes over the electromagnetic coil portion 47. Therefore, the displaced end portion of the bimetal 51 is never engaged with the electromagnetic coil portion 47 and the bimetal can be protected. This realizes precise control on a relative distance between the bimetal 51 and the bridge wire 52 in the axial direction of the electromagnetic clutch, making it possible to protect the bimetal 51 even when the bimetal 51 is largely displaced and also to considerably improve the reliability of the energization interrupting device.
The inner wall 41d, the outer wall 41e, the inner abutment portion 41f, and the outer abutment portion 41g integrally form the bobbin 41. Thus, the bridge wire 52 can be easily obtained in the process for winding the electromagnetic coil 42 around the bobbin 41. This realizes cost reduction of the electromagnetic clutch 1 even though the energization interrupting device is provided.
While the above embodiment shows an example where the bimetal is used as a thermally-actuated element, other thermally-actuated elements such as shape memory alloy are applicable. Further, although the above embodiment shows an example where the electromagnetic clutch is attached to the compressor used for the in-vehicle air conditioner, the electromagnetic clutch can be used for the other purposes without any limitation.
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/077386 | 10/8/2013 | WO | 00 |