Rotor for vehicle dynamo

Abstract: A rotor for a vehicle dynamo includes a field coil bobbin (6) provided with ventilation slots (6a) and a heat conductive material (7) provided between the bobbin and the field cores, whereby the heat radiation from the field coil is increased.

Description: The present invention relates to rotors for vehicle dynamos. A conventional rotor of a vehicle dynamo is shown in FIG. 4. The rotor consists of a rotary shaft 3; a pair of field cores 1 and 2 secured to the rotary shaft 3 such that pole claws 1a and 2a each extending inwardly from the free end thereof alternately mesh each other to form an annular channel; a bobbin 4 mounted in the annular channel; and a field coil 5 placed in the bobbin 4. When rotation is transmitted to the rotary shaft 3 via a driving pulley (not shown) to rotate the rotor,' with a field current supplied to the field coil 5 by a current collector (not shown), power is generated in a fixed coil (not shown) mounted around the rotor. The field coil 5 of the conventional dynamo suffers from high temperatures arising from the heat generation or reception. When the field coil is at high temperatures, the electrical resistance becomes high, making the field current and the magnetomotive force lower. As a result, the output current of the vehicle dynamo is lower than the output current in cold conditions, as shown in FIG. 5. The output current in a high-temperature atmosphere is also lower than the ouput current in a normal-temperature atmosphere as shown in FIG. 6. FR-A-2556147 discloses a vehicle dynamo rotor comprising field cores with plurality of pole claws extending inwardly and interdigitated, forming within them an annular channel, a bobbin in the annular channel having a cylindrical portion and a pair of opposed flange portions, and a field coil on the bobbin. This document also proposes the provision of heat-conductive material between the bobbin and the field cores. However these measures alone do not adequately protect the field coil from impaired performance in hot conditions. It is an object of the invention to provide a rotor for a vehicle dynamo, which is resistant to a decrease in output current in a high-temperature atmosphere without changing the frame or copper quantity of the vehicle dynamo. According to the invention there is provided a rotor for a vehicle dynamo comprising a pair of field cores so disposed that a plurality of pole claws extending inwardly from a free end of each field core are interdigitated with each other and form within them an annular channel, a bobbin placed in the annular channel and having a cylindrical portion and a pair of opposed flange portions, a field coil placed on the bobbin, and heat-conductive material between the field coil and the field cores, characterized in that the bobbin is provided with at least one internal ventilation opening in the cylindrical portion and/or flanges. The above and other objects, features, and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. FIG. 1 is a sectional view of the rotor of a vehicle dynamo according to an embodiment of the invention; FIG 2 is an elevational view of a bobbin useful for the rotor of FIG. 1; FIG. 3 is a top view of the bobbin of FIG. 2; FIG. 4 is a sectional view of the rotor of a conventional vehicle dynamo; FIG: 5 is a graph showing the relation between the output current and the speed of the conventional rotor in cold and hot conditions; and FIG. 6 is a graph showing the relation between the output current and the speed of the conventional rotor in different ambient temperatures. In FIG. 1, the rotor of a vehicle dynamo consists of a rotary shaft 3; a pair of field cores 1 and 2 secured to the rotary shaft 3 such that pole claws 1a and 2b each extending inwardly from the free end thereof alternatively mesh each other to form an annular channel; a bobbin 6 mounted in the annular channel; and a field coil 5 placed in the bobbin 6. As best shown in FIGS. 2 and 3, the bobbin 6 has a number of ventilation slots 6a each having an axial portion extending in the axial direction on a cylindrical portion 6c and a pair of radial portions extending on opposed flange portions 6b in the radial direction from opposite ends of the axial portion. A heat conductive material 7 is placed between the bobbin 6 and the field cores 1 and 2. The heat generated in or received by the field coil 5 is transmitted to the field cores 1 and 2 via the ventilation slots 6a or the bobbin 6 and the heat conductive material 7 between the bobbin 6 and the field cores 1 and 2. Consequently, an increase in temperature of the field coil 5 is controlled to minimize an increase in the electrical resistance so that a decrease in the output current due to the decreased field current in hot conditions or in a high atmosphere is minimized. Alternatively, the ventilation slots 6a may be circular or polygonal openings. The ventilation openings 6a may be provided on either the flange portions 6b or the cylindrical portion 6c only. As has been described above, with the ventilation openings provided on the field coil bobbin according to the invention, it is possible to minimize a decrease in magnetomotive force due to an increase in temperature of the field coil so that it is possible to minimize a decrease in the output current in hot conditions or in a high temperature atmosphere without changing the frame or copper quantity of the charging dynamo for vehicles.

Claims: A rotor for a vehicle dynamo comprising a pair of field cores (1, 2) so disposed that a plurality of pole claws (1a, 2b) extending inwardly from a free end of each field core are interdigitated with each other and form within them an annular channel, a bobbin (6) placed in the annular channel and having a cylindrical portion and a pair of opposed flange portions, a field coil (5) placed on the bobbin, and heat-conductive material (7) between the field coil and the field cores, characterized in that the bobbin is provided with at least one internal ventilation opening (6a) in the cylindrical portion and/or flanges. A rotor of Claim 1, wherein said bobbin (6) has a plurality of ventilation openings (6a) each composed of a slot consisting of an axial portion extending in the axial direction in said cylindrical portion and a pair of opposed radial portions extending in said flange portions in the radial direction from opposite ends of said axial portion.

Inventors: KUSUMOTO KATSUHIKO C O MITSUBI, MORIKAKU HIDEKI C O MITSUBISHI, KUSUMOTO, KATSUHIKO, MORIKAKU, HIDEKI, KUSUMOTO, KATSUHIKO, C/O MITSUBISHI DENKI K.K., MORIKAKU, HIDEKI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: H02K1
IPC codes: H02K1, H02K9, H02K3