Electromagnetic powder coupling device

Abstract: An electromagnetic powder coupling device which can be used either as a brake or a clutch has a blower (31) and a plurality of passages (39b,39c,35b) for forced draft air cooling.

Description: The present invention generally relates to an electromagnetic powder coupling device, and more particularly to a cooling system applicable to an electromagnetic powder coupling device including a clutch and or a brake. Major components of the general type industrial electromagnetic powder coupling device consist of a field assembly incorporating therein a magnetic coil, a driving clutch member referred to as a cylinder, a rotor as a driven clutch member and magnetic powder, merely referred to as "powder" being filled in a gap defined between the cylinder as the driving clutch member and the driven clutch member, which gap is usually referred to an actuating gap. We will now explain with reference to Fig. 1, the general function of an electromagnetic powder coupling device. When a cylinder 5 is rotated by being driven by an external driving shaft or by an attached driving shaft 4, with the coil 8 of a field member 9 not being excited, the powder in the gap is urged by centrifugal force against the inner wall of the cylinder 5, and thus an annular space is formed between the coalesced surface of the magnetic powder and a rotor 10. Therefore no appreciable amount of torque can be transmitted from the cylinder to the rotor, in this state of no contact between the powder and the rotor 10. On the other hand, when the field coil 8 is excited, a closed path of magnetic flux  is established as shown by a dash line in Fig. 1. Field member → Cylinder → Rotor → Cylinder → Field member Then the magnetic powder aligns in the gap along the path of the magnetic flux  in the assembly and couples the cylinder 5 with the rotor 10, thereby the driving force can be transmitted from the cylinder 5 to the rotor by virtue of the shear resistance of the magnetic powder. Since Fig. 1 is shown as an electromagnetic powder brake the rotor 10 is held stationary by a fixed rotor boss 10c, however, if this coupling device is to be used as a clutch, the rotor 10 is connected to an output shaft (not shown) which can be rotatable integrally with the rotor 10. Because of the fact that it utilises magnetic powder as a power transmitting medium, the coupling devices of this kind are capable of imparting constant torque even under slipping conditions which other coupling means cannot achieve. They can be operated with stable control under conditions of continuous slip. However, the most important problem to be solved is how to cool and remove the heat generated by the aforesaid continuous slip which is not encountered in any other friction disc type coupling means. In view of the above-mentioned problem, there have been proposed a number of cooling systems up to the present, such as water cooled, natural cooling and forced draft air cooling using an air blower or blowers, among which the water cooling has been found to be satisfactory so far as its cooling efficiency is concerned. However, water cooling has been found to have several drawbacks, such as troublesome work involved in the provision of piping, leakage of water in use, and the related parts of the device becoming liable to be dewed. To solve the drawbacks encountered in the water cooling system of the prior art, as mentioned above, a natural cooling means as shown in Fig. 1 has been proposed, which radiates both frictional heat and Joule heat generated by a rotor 10 and a cylinder 5 through the surfaces of a bracket 2 and a bracket 3 contacting the surrounding atmosphere. It also dissipates the Joule heat generated by the field member 9 through the surface of the field member 9. US-A-4085344, which represents the prior art as referred to in the preamble of claim 1, discloses a magnetic clutch having a forced air draft type cooling means. The clutch has a plurality of axially and radially extending channels through the stator member. Shown in Fig. 2 is a forced air draft type cooling means adopted in an electromagnetic powder brake capable of cooling its field member 9 and brackets 22 for holding the field member 9 and having no such appreciable drawbacks as found in the water cooling system as mentioned above. As shown in Fig. 2, the cooling means comprises, a blower 1 attached to the bracket 22 disposed at the output side of the coupling device, and a cooling fin 5a supported by a bracket 26 rotatable integral with the input shaft 4 and positioned axially outside the cylinder 5 and at the portion between the blower 1 and the cylinder 5. The cooling means further comprises a heat pipe 20a of high heat conductive material and including a cooling fin 20b which is secured to and is in tight contact with the rotor 20 at its axially central portion and axially extends toward the outlet of aforesaid blower 1. Provided at the input side is an input shaft 4 which usually is an external driving shaft to be connected at the user's site. The cylinder 5 is fixed to the input shaft 4 through a side plate 7 and is spaced apart by the outer periphery of the rotor 20 by a gap of a specified size. As can be seen from Fig. 1, such a cooling system which dissipates heat generated by means of heat conduction through the contact with air at the surface or surfaces of the brackets at both axial ends and the surface of the field member, amounts to no more than a natural cooling system. As a consequence, cooling effect of such cooling system cannot be expected to be high enough and the efficiency in slippage also becomes low, which gives rise to a lower allowable work capacity than that of a water cooled system. As to the forced draft cooling system shown in Fig. 2, the parts which are effective for cooling are the heat pipe 20a and fin 20b for cooling the rotor 20 and bracket 22, and the fin 5a for cooling the cylinder 5. Therefore, the cooling air from the blower 1 flows, as a uniform stream K, passing through the fin 20b then flows somewhat slantedly in radial direction outwards. As a consequence, the heat generated at the actuating part of the coupling device is transmitted to the field member 9 through the bracket 22. In addition, Joule heat generated at the coil is also passed to the field member 9, and so the cooling power becomes insufficient. This results in lower slip efficiency as compared with that obtainable by the water cooled system. By taking the aforesaid drawbacks in the conventional cooling system into consideration, the present invention aims to obviate such drawbacks and to provide an improved cooling system. Accordingly, the present invention seeks to increase the cooling effect of the prior art coupling device which has relied only on natural cooling as shown in Fig. 1, in which the effect of cooling was found to be insufficient. Therefore, according to the present invention an electromagnetic powder coupling device to be used as a clutch or a brake for transmitting or braking the torque imparted by an external drive shaft which comprises: a pair of brackets at the input and output side of the device respectively; a field member, consisting of a yoke and a coil assembly, being tightly received by said brackets at both of its axial ends; a hollow cylinder coaxially disposed in the inner space of the field member and being supported by a pair of side plates each being disposed at each axial end of said cylinder so as to be integrally rotatable with the drive shaft; a rotor disposed coaxially around the axis of rotation and axially between said side plates; an annular magnetic flux shielding ring of non-magnetic material radially inserted through said cylinder substantially at the central part of said cylinder; magnetic powder filling a space between said cylinder and said rotor, for effecting magnetic coupling between said cylinder and said rotor when said field member is excited, and for releasing the magnetic coupling when said field member is not excited; a blower for generating a cooling draft and a plurality of vent channels for directing the cooling draft; the cooling of the heat generated by Joule heat and frictional heat emanated by the related parts of the coupling device being effected by natural cooling through the outer surface of the parts or component; said brackets at each axial end being radially extended so that they define at least an air space of sufficient inner volume; wherein: that blower is disposed at the radially outer peripheral end of said brackets for blowing a draft of cooling air toward said field member and in that the plurality of vent channels consists of two kinds of air paths formed through said field member, a first path generally passing through the interior of said field member along the outer surfaces of the coil assembly at the axial ends both at the input side and the output side and slantly toward the axial centre of said cylinder, then passing axially through the interior of said cylinder in opposite directions toward said input side and output side, and a second path which radially passing through said field member at the place adjacent to the both axial ends at the input side and output side and straightly flowing down to the outlet opened at the reverse side of said field member adjacent to the outlets of said former path; whereby the draft of cooling air passes through a pair of exit vents having openings at each of the brackets at the input side and the output side and at the portion substantially corresponding to the outlets of said two kinds of air paths. An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a half cut cross-sectional front view showing an electromagnetic powder brake of a prior art type using natural cooling system; Fig. 2 is a half cut cross-sectional front view showing an electromagnetic powder brake of another type prior art one using forced draft cooling system; Fig. 3 is a half cut cross-sectional front view showing an electromagnetic powder coupling device according to an embodiment of the present invention; Fig. 4 is an enlarged perspective partial view taken along arrow mark IV of Fig. 3. Referring now to Figs. 3 and 4, one or more blowers 31 incorporating therein a driving means such as a motor (not shown) are disposed on the radially outer periphery defined by brackets 32 and 33. Brackets 32 and 33 for supporting a hollow cylinder 35, each one of which is attached to each opposite axial end of the coupling device, are radially and outwardly extended, and a top plate, namely, an outer peripheral wall connecting the radially outer ends of the thus extended two brackets 32 and 33, is provided. A top cover 39e covering the inner chamber which houses the coil assembly 8, is penetrated radially by one or more groups of vent channels, each channel consisting of one vent opening 39b of large diameter opening at the axially central part of the top cover 39e and a pair of small vents 39c, each one opening at each axial end of the top cover 39e. The vent opening 39b opens through the top cover 39e so that it can be in communication with the inner part of the field member 39 through at least a pair of vent grooves 39d, each formed axially in the coil member 8 at a suitable position in the coil assembly 8 such as in the field member 39 and takes a somewhat complicated path along the outer surface of the coil at both axial sides, and then these vent grooves 39d are directed slantedly and axially inward to a ring 35' for shielding magnetic flux (hereinafter merely referred to shielding ring) which acts to prevent magnetic flux from taking a short cut path through the cylinder 35, which will be explained later. The pair of small vents 39c each of which open near each axial end of the top cover 39e, runs directly radially inwardly toward the inner end of the field member 39 and toward the axial end of the cylinder 35. The vent opening 39b and the pair of small vents 39c, are in alignment with each other in an axial direction. The cylinder 35 generally has a hollow cylindrical shape, and is formed with at least one, preferably with a plurality of, axially opened vent passages 35b circumferentially spaced apart as holes or sectored apertures. Each of these vent passages 35b, passes axially through the peripheral wall of the cylinder 35. The shielding rings 35' inserted radially at the axial central part of the cylinder are partly cut away to such an extent that they constitute plural vent recesses 35c each of which intersects aforesaid axially opened vent passages 35b of the cylinder 35 so that each of the vent passages 35b can communicate with the pair of vent grooves 39d and finally with the air space 31c defined at the outlet of the blower 31. Since the vent passages 35b are opened through the peripheral wall of the cylinder 5 and each axial end of the vent passage 35b confronts the side wall of the brackets 32 and 33 at each axial side of the coupling device, and each side wall of the brackets 32 and 33 is opened to have a through hole as an exit vent 32b or 33b in communication with the spaces 32e and 33e, respectively, formed between the side plate 6 and the bracket 32 itself, and similarly between the side plate 7 and the bracket 33 itself, each of these exit vents 32b and 33b can communicate with the small vents 39c at either axial end of the field member 9 and eventually with the air draft coming from the blower 31. On the other hand, each of the aforesaid vent opening 39b at the central part of the top cover 39e of the field member 39 can be in communication with either one of the exit vents 32b or 33b by flowing through either one half axial part of the vent passage 35b. Now, operation of the cooling means embodiment will be explained. To make the manner of air flow clear the following explanation will be made with respect to only one blower in the coupling device, related vent channels consisting of a number of various types of openings provided for passing the cooling air blown from the blower 31. The air radially blown from each blower 31 is divided into three radial streams all passing through the field member 39, namely, a main central stream B which flows by passing through the central vent opening 39b of the field member and two branch side streams A each of them also radially passes through the pair of small vents 39c opened near the opposite axial ends of the field member 39. The air blown into the vent opening 39b as a main stream B flows through the vent opening 39b, then the air flow is divided into two radial streams each flowing through two somewhat winding paths along the outer surface of the coil assembly and to the central part of the radially inner part of the field member where the shielding ring 35' is disposed. The air flows through the winding recesses along the both outer marginal surfaces of the coil assembly merges again into a single stream, in the vent recess 35c of the drilled part of the shielding ring 35', but the air having passed through the vent recess 35c is immediately divided again into two axial streams, one directed to the input side and the other to the output side, and each flows axially through each of the two half parts of the vent passage 35b down to the outlet, where the cooling air flowing through the vent passage 35b in two opposite direction is allowed to exit outside from each of the exit vent 32b and 33b opened through each side wall of the brackets at both sides. As explained above, the air cooling system can be readily provided by radially extending brackets at both axial ends and providing one or more blowers on the peripheral wall of the thus extended brackets and by forming a plurality of vent channels which can be classified into two paths, a first one of a central path comprising vent opening 39b, vent grooves 39d, vent recess 35c and vent passage 35b, thereby allowing the air blown from the blower to flow as a central stream B flowing radially through the central part and then takes two axial flows toward the exit vents at both axial ends, and a second branch path passing through both the axial end of the field member and directly toward the vent gates and allows the blown air to flow as a second stream A. As a consequence, Joule heat at the field member, frictional heat combined with Joule heat at the cylinder and the rotor can be effectively removed without being accompanied by any problems such as in piping work, water leakage and dew forming foundin the water cooling system.

Claims: An electromagnetic powder coupling device to be used as a clutch or a brake for transmitting or braking the torque imparted by an external drive shaft which comprises: a pair of brackets (33,32) at the input and output side of the device respectively; a field member (39), consisting of a yoke and a coil assembly (8), being tightly received by said brackets at both of its axial ends; a hollow cylinder (35) coaxially disposed in the inner space of the field member and being supported by a pair of side plates each being disposed at each axial end of said cylinder (35) so as to be integrally rotatable with the drive shaft; a rotor (10) disposed coaxially around the axis of rotation and axially between said side plates; an annular magnetic flux shielding ring (35') of non-magnetic material radially inserted through said cylinder substantially at the central part of said cylinder; magnetic powder (5b) filling a space between said cylinder (35) and said rotor (10), for effecting magnetic coupling between said cylinder (35) and said rotor (10) when said field member (39) is excited, and for releasing the magnetic coupling when said field member (39) is not excited; a blower for generating a cooling draft and a plurality of vent channels for directing the cooling draft; the cooling of the heat generated by Joule heat and frictional heat emanated by the related parts of the coupling device being effected by natural cooling through the outer surface of the parts or component; said brackets (33,32) at each axial end being radially extended so that they define at least an air space of sufficient inner volume; characterised in that: that blower (31) is disposed at the radially outer peripheral end of said brackets (33,32) for blowing a draft of cooling air toward said field member (39) and in that the plurality of vent channels consists of two kinds of air paths formed through said field member (39), a first path (39d) generally passing through the interior of said field member along the outer surfaces of the coil assembly (8) at the axial ends both at the input side and the output side and slantly toward the axial centre of said cylinder (35), then passing axially through the interior of said cylinder (35) in opposite directions toward said input side and output side, and a second path (39c) which radially passing through said field member (39) at the place adjacent to the both axial ends at the input side and output side and straightly flowing down to the outlet opened at the reverse side of said field member (39) adjacent to the outlets of said former path; whereby the draft of cooling air passes through a pair of exit vents having openings at each of the brackets (33,32) at the input side and the output side and at the portion substantially corresponding to the outlets of said two kinds of air paths.

Inventors: MAJI HIROSHI, TUJI HIDEHISA, YAMAJI HIROYOSHI, MAJI, HIROSHI, TUJI, HIDEHISA, YAMAJI, HIROYOSHI
Applicants: SHINKO ELECTRIC CO LTD, SHINKO DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: F16D37
IPC codes: F16D63, F16D37