Rotary electric machine for vehicles

A rotary electric machine for vehicles is provided, which includes a rotor, a stator disposed opposed to the rotor, a frame made of aluminum and supporting the rotor and the stator, and a rectifier secured to an outer end face of the frame and having low-loss elements as rectifying elements. A heat insulator is disposed between the rectifier and the frame. With this configuration, deterioration can be prevented in the overall cooling properties, while at the same time the cooling properties of the rectifier can be enhanced.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2008-174051 filed Jul. 3, 2008, the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary electric machine which is loaded on vehicles, such as passenger cars and trucks.

2. Related Art

A type of rectifier that has been known is disclosed in Japanese Patent Application Laid-Open Publication No. 2002-519987, for example. This type of rectifier has a two-layer structure in which a positive fin (positive heat sink) and a negative fin (negative heat sink) are disposed along the direction of the rotary shaft. In this type of rectifier, the base portion of each of negative diodes is press-fitted to the negative fin so as to be projected out of the end face of the negative fin into the direction of the frame, for direct contact with the base of the frame. With this structure, the heat generated by the negative diodes can be transferred to the frame to enhance the cooling properties.

Also, a type of vehicle alternator that has been known is disclosed in Japanese Patent Application Laid-Open Publication No. 06-078504, for example. This type of vehicle alternator has a structure in which a heat-reflective member is disposed at an inner peripheral surface of the frame (rear bracket), which surface faces the stator coil, via a heat insulator. With this structure, heat can radiate effectively from the diodes of the rectifier to the frame (rear bracket).

The structure disclosed in Japanese Patent Application Laid-Open Publication No. 2002-519987 is based on the premise that the temperature of the rectifier is higher than that of the frame. Accordingly, if the temperature of the rectifier becomes lower than that of the frame due to reduction of electrical resistance of the rectifying elements, for example, heat will contrarily be transferred from the frame to the rectifier.

As a result, the temperature of the rectifier will be undesirably raised due to the heat transferred from the frame. A countermeasure that can be taken for reducing the temperature of the frame in this case may be to combine the structure disclose in Japanese Patent Application Laid-Open Publication No. 06-078504 with the structure disclosed in Japanese Patent Application Laid-Open Publication No. 2002-519987.

However, preventing the heat transfer from the stator coil to the frame may hinder cooling of the stator coil, because the cooling is actually produced by permitting the heat to escape from the stator coil to the frame. Thus, when the above structures are combined, concerns may arise that the cooling properties of the entire vehicle alternator may be deteriorated. Therefore, the countermeasure mentioned above may not be preferable.

SUMMARY OF THE INVENTION

The present invention has been made in light of the problem mentioned above, and has as its object to provide a rotary electric machine for vehicles which is able to prevent deterioration in overall cooling properties and to enhance the cooling properties of the rectifier.

In order to solve the problem explained above, the rotary electric machine for vehicles of the present invention comprises a rotor, a stator disposed opposed to the rotor, a frame made of aluminum and supporting the rotor and the stator, a rectifier secured to an outer end face of the frame and having low-loss elements used as rectifying elements, and a heat insulator disposed between the rectifier and the frame.

Use of the low-loss elements can reduce the amount of heat generated by the rectifier per se. Also, by arranging the heat insulator between the rectifier and the frame, the heat radiated from the frame can be shielded by the heat insulator, whereby the cooling properties of the rectifier can be enhanced. In addition, the heat generated in the stator of the rotary electric machine for vehicles can be transferred to the frame, whereby the overall cooling properties can be prevented from being deteriorated.

It is preferred that the low-loss elements mentioned above are low-loss diodes. Alternatively, it is preferred that the low-loss elements mentioned above are MOS transistors. Use of these elements can reduce losses during power on, compared with the generally used silicon diodes.

It is preferred that the heat insulator mentioned above is formed of a material having heat conductivity smaller than that of aluminum. Thus, compared with the case where a frame made of aluminum is directly secured to a rectifier, the cooling properties of the rectifier can be enhanced because the heat from the frame can be reduced.

It is preferred that the heat insulator mentioned above is formed of stainless steel, ceramic, a resin, or glass.

The heat insulator may be formed easily by using each of these materials. Further, concurrently with the heat insulation, use of stainless steel, for example, as an electrically conductive material for forming the heat insulator, may enable electrical connection between a negative-side radiator plate of the rectifier and the frame. In addition, concurrently with the heat insulation, use of a resin, for example, as an electrically insulating material for forming the heat insulator, may ensure electrical insulation between a positive-side radiator plate of the rectifier and the frame.

It is preferred that the heat insulator is provided as a gap which is formed by locating both the rectifier and the frame to be spatially apart from each other by a distance corresponding to the gap. This may contribute to reducing the number of parts to thereby reduce the cost. At the same time, by utilizing the heat insulator (the gap) as a passage for cooling air, the amount of cooling air can be increased.

It is preferred that the rectifier is secured to the frame by means of a screw which is formed of a material having heat conductivity smaller than that of aluminum. The material may be stainless steel. This may reduce the heat that will be transferred to the rectifier from the frame via the screw used for securing the rectifier to the frame.

It is desirable that the rectifier comprises a positive-side radiator plate joined with positive-side rectifying elements and a negative-side radiator plate joined with negative-side rectifying elements; the negative-side radiator plate is disposed opposed to the frame with an interposition of the heat insulator; and the heat insulator is formed of an electrically conductive material to establish electrical connection between the negative-side radiator plate and frame via the heat insulator. In particular, it is preferred that the heat insulator is an electrically conductive body having a hollow structure. Use of such a heat insulator may enable heat insulation between the rectifier and the frame, concurrently with the electrical connection therebetween.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, hereinafter will be described in detail an embodiment of a vehicle alternator to which a rotary electric machine for vehicles of the present invention is applied.

FIG. 1is a cross-sectional view illustrating a general configuration of a vehicle alternator according to an embodiment of the present invention. A vehicle alternator1shown inFIG. 1includes a stator2, a rotor3, a brush device4, a rectifier5, a frame6, a rear cover7and a pulley8.

The stator2includes a stator core21, and a three-phase stator winding23which is wound about the stator core21at predetermined intervals, while being disposed in a plurality of slots formed in the stator core. The rotor3includes a field winding31made up of an insulated copper wire which is coaxially wound to have a cylindrical shape, and pole cores32each having a plurality of pole claws. The field winding31is laterally sandwiched between the pole cores32with a rotary shaft33passing through the pole cores. A cooling fan34is attached such as by welding to an end face of the front-side pole core32. Similarly, a cooling fan35is attached such as by welding to the rear-side pole core32.

The brush device4plays a role of passing excitation current from the rectifier5to the field winding31of the rotor3, and includes brushes41,42pressed against slip rings36,37, respectively, formed at the rotary shaft33of the rotor3.

The rectifier5, which is secured to an outer end face of the frame6, plays a role of rectifying the three-phase AC voltage that is the output voltage from the three-phase stator winding23to obtain DC output power. The rectifier5is configured being provided with a terminal block51containing therein wiring electrodes, positive- and negative-side radiator plates52,53which are disposed with a predetermined interval therebetween, and a plurality of rectifying elements serving as low-loss elements. The rectifying elements are press-fitted to press-fitting bores formed in each of the radiator plates.

The frame6accommodates the stator2and the rotor3. The rotor3is supported by the frame6so as to be rotatable about the rotary shaft33. Meanwhile, the stator2is secured to the frame6so as to be disposed on the outer peripheral side of the pole cores32of the rotor3, being apart from the rotor3by a predetermined distance. The frame6includes outlet and inlet windows61,62for cooling air. The outlet window61is provided at a portion facing the stator winding23which is projected from an axial end face of the stator core21. The inlet window62is provided at each axial end face of the frame6.

The rear cover7entirely covers, for protection, the brush device4, the rectifier5and a controller12, which are all mounted outside the frame6on the rear side. The rear cover7has an axial end face corresponding to an area facing the rectifier5. In this area of the axial end face, a plurality of inlet windows (not shown) are formed to introduce cooling air into the rear cover7with the rotation of the rear-side cooling fan35.

In the vehicle alternator1having the structure as explained above, the rotor3is designed to rotate in a predetermined direction, when torque is given to the pulley8by an engine (not shown) via a belt or the like. When excitation voltage is applied from outside, in this state, to the field winding31of the rotor3, the claws of each of the pole cores32are excited to generate three-phase AC voltage across the stator winding23. Resultantly, DC output power can be derived from an output terminal of the rectifier5.

FIG. 2is a connection wiring diagram illustrating the vehicle alternator1. The rectifying elements used in the rectifier of the present embodiment are MOS transistors5a-5fhaving less loss than generally used silicon diodes during power on. The controller12performs on/off control of the excitation current to be passed to the field winding31. At the same time, the controller12controls the timing for supplying current to the six MOS transistors5a-5fprovided at the rectifier5. Of the six MOS transistors5a-5f, three MOS transistors5a-5care joined to the positive-side radiator plate52and the remaining three MOS transistors5d-5fare joined to the negative-side radiator plate53.

The MOS transistors5a-5fhaving less loss than generally used silicon diodes during power on as mentioned above, can suppress the amount of heat generated by the rectifier5. Therefore, the temperature of the negative-side radiator plate53of the rectifier5, which is located on the side of the frame6, can be made lower than the temperature of the frame6. In the present embodiment, a heat insulator60is disposed between the frame6and the rectifier5to prevent heat transfer from the frame6having higher temperature to the rectifier5even in such a case. The heat insulator60is disposed being clamped between the frame6and the negative-side radiator plate53of the rectifier5.

Specifically, the heat insulator60may be formed using such a material as stainless steel, ceramic, resin or glass, or a material obtained by combining these materials. The heat insulator60may be formed easily by using each of these materials. Further, interposition of the heat insulator60may easily shield the negative-side radiator plate53from heat radiated from the frame6, compared with the case where the radiator plate53is directly brought into contact with the frame6. In addition, concurrently with the heat insulation, use of stainless steel, an electrically conductive material, as the heat insulator60, can establish electrical connection for grounding between the negative-side radiator plate53and the frame6.

Alternatively, a simple gap may be provided between the frame6and the negative-side radiator plate53to serve as the heat insulator60, instead of using a member made of the materials, such as stainless steel, mentioned above. Formation of such a gap can decrease the number of parts and the cost, and may increase the amount of cooling air when the heat insulator60(the gap) is used as a passage of cooling air.

The present embodiment uses the heat insulator60in order to reduce heat transfer between the rectifier5and the frame6. Therefore, this may require a scheme for also reducing heat transfer in securing the rectifier5to the frame6. In particular, the need that the negative-side radiator plate53has to be electrically and directly connected to the frame6, necessitates the cutoff of the heat therebetween.

FIG. 3Ais a schematic partial cross-sectional view illustrating a partial structure in which the negative-side radiator53of the rectifier5is secured to the frame6by means of a screw, andFIG. 3Bis a cross-sectional view illustrating a whole image of the negative-side radiator of a rectifier;

In the structure shown inFIG. 3A, the heat insulator60is interposed between the negative-side radiator plate53and the frame6, and in this state, the radiator plate53is fixed to the frame6by means of a screw161made of stainless steel. Use of the stainless steel screw161can suppress the heat transfer from the frame6to the radiator plate53via the screw161. In this case, an electrical connection can be established between the negative-side radiator plate53and the frame6via the screw161. If an electrically conductive material of stainless steel is used for the heat insulator60, the electrical resistance between the negative-side radiator plate53and the frame6can be further reduced.

FIGS. 4A and 4Bshow another example of the heat insulator60that is an electrically conductive body.FIG. 4Ais a perspective view illustrating the heat insulator60A made of a metallic material and having a columnar shape with a through bore being formed at the center thereof.FIG. 4Bis a perspective view including a vertical cross section of the heat insulator60A shown inFIG. 4A. A hollow structure as shown inFIG. 4Bcan exert a heat insulating effect. Use of a metallic material, such as stainless steel, that can suppress heat transfer may enhance the heat insulating effect exerted by the hollow structure. The through bore at the center is used for passing the screw161shown inFIG. 3Atherethrough. Depending on the positions where the radiator plate60is used, use of the screw161can be omitted. Accordingly, depending on the positions, formation of the through bore may be omitted, or the columnar shape may be changed to a different shape.

FIG. 5is a partial cross-sectional view illustrating an example of electrical connection for grounding between the negative-side radiator plate53and the frame6in the case where the heat insulator60B is provided in the form of a gap. In the structure shown inFIG. 5, while the heat insulator60B is a gap, the electrical connection for grounding between the negative-side radiator plate53and the frame6is established using a conductor wire162. As shown, washers163are provided at both ends of the conductor wire162and secured to the radiator plate53and the frame6by tightening respective screws164. The conductor wire162may be fixed by welding or soldering.

As described above, in the vehicle alternator1according to the present embodiment, use of the MOS transistors as the low-loss elements can reduce the amount of heat generated by the rectifier5per se. In addition, arrangement of the heat insulator60between the rectifier5and the frame6can cut off the heat emitted from the frame6. As a result, the cooling properties of the rectifier5can be enhanced. Also, since the heat produced by the stator2of the alternator1can be transferred to the frame6, deterioration can be prevented in the cooling properties of the alternator1as a whole.

The present invention is not intended to be limited to the above embodiment, but may be modified in various manners without departing from the spirit of the present invention.

The above embodiment has exemplified the rectifier5in which the negative-side radiator plate53is disposed on the side of the frame6. However, the present invention may be applied to a rectifier in which the positive-side radiator plate52is disposed on the side of the frame6. In this case, an insulating material of ceramic, resin or glass may be used for the heat insulator60to ensure electrical insulation between the positive-side radiator52of the rectifier and the frame6, concurrently with the heat insulation. Also, in this case, the electrical connection for grounding between the negative-side radiator plate53and the frame6may be established via a stud bolt65(seeFIG. 1) extending from the frame6. It is desirable that the stud bolt65is made of a material, such as stainless steel, that suppresses heat transfer.

As a matter of course, the present invention may be applied to a rectifier in which the MOS transistors are mounted on a single power board.

In the above embodiment, the rectifier5has been configured using the MOS transistors5a-5fas the low-loss elements. Alternatively, other low-loss elements, such as low-loss diodes, may be used to configure a rectifier.

In the above embodiment, the description has been given on the vehicle alternator1having a function of electric generation. However, the present invention may be applied to a rotary electric machine for vehicles having functions of a generator and a motor. In this case, the controller12may effect control in such a way that the rectifier5can operate as an inverter to apply three-phase AC voltage to the stator winding23, for rotation of the rotor3.

In the above embodiment, stainless steel has been used as an example of a material having heat conductivity smaller than that of aluminum. However, other materials may be used.