Electric power steering apparatus

A control unit including a plurality of boards is formed of a single multilayer metal substrate, whereby an electric power steering apparatus can be obtained in which connection members for connecting between the boards are made unnecessary, so the size and cost of the apparatus can be reduced, and the reliability of bonding can be improved. In the electric power steering apparatus, a power main body (20a) and a control main body (20b) are mounted on a metal substrate (22), and the power main body (20a) and the control main body (20b) are electrically connected to each other by wiring patterns (26a through 26e) and metal columns 28a through 28d in the metal substrate 22.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power steering apparatus equipped with an electric motor for outputting assist torque to the steering wheel of a vehicle, and a control unit for controlling the driving of the electric motor.

2. Description of the Related Art

In the past, there has been known an electric power steering apparatus which is equipped with an electric motor for outputting assist torque to the steering wheel of a vehicle, and a control unit mounted on the electric motor for controlling the driving of the electric motor (see, for example, a first patent document (Japanese patent No. 3638269).

This electric power steering apparatus includes a power board on which a bridge circuit is mounted for switching the current of the electric motor, a control board on which a microcomputer is mounted for generating a drive signal to control the bridge circuit, and a high current board on which a conductive plate forming a high current wiring pattern is insert molded and on which a capacitor is mounted for absorbing current ripples, wherein the power board, the high current board and the control board are stacked or laminated one over another in this order so as to form a three-layer structure.

In the above-mentioned electric power steering apparatus, the control unit has a substrate comprising the three boards, i.e., the power board, the high current board and the control board, which are laminated one over another in this order to form the three-layer structure. Accordingly, the height of the control unit becomes large, and connecting members for connecting these boards with one another are required at the same time, resulting in increased connection or joint portions.

As a result, there arises a problem that the apparatus becomes large in size, high in cost, and low in reliability of electrical connections.

SUMMARY OF THE INVENTION

Accordingly, the present invention is intended to obviate the problem as referred to above, and has its object to provide an electric power steering apparatus which can be reduced in size and cost, and improved in reliability of electrical connections by constructing a power board, a high current board and a control board by the use of a single substrate.

Bearing the above object in mined, according to the present invention, there is provided an electric power steering apparatus including an electric motor for outputting assist torque to a steering wheel of a vehicle, and a control unit for controlling the driving of the electric motor. The control unit includes: a power main body that includes a bridge circuit composed of a plurality of semiconductor switching elements for switching a current supplied to the electric motor in accordance with torque assisting the steering wheel; a control main body that generates a drive signal to control the bridge circuit based on the steering torque of the steering wheel; a metal substrate that is composed of a plurality of insulating layers and a plurality of conductive layers having wiring patterns respectively formed thereon, the insulating layers and the conductive layers being alternately laminated one over another on a metal plate; and a heat sink with the metal substrate being fixedly attached thereto. The power main body and the control main body are arranged on the same surface of the metal substrate, and the power main body and the control main body are electrically connected to each other through the metal substrate.

According to the electric power steering apparatus of the present invention, the power main body and the control main body are mounted on the single metal substrate, so the apparatus can be reduced in size and cost, and the reliability of electrical connections can be improved.

The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described in detail while referring to the accompanying drawings. In the respective embodiments, the same or corresponding members or parts are identified by the same reference numerals or characters.

FIG. 1is a cross sectional view that shows an electric power steering apparatus according to a first embodiment of the present invention.FIG. 2is an exploded perspective view that shows the electric power steering apparatus inFIG. 1, andFIG. 3is an exploded perspective view that shows a control unit20inFIG. 2.

In these figures, an electric motor1in the form of a three-phase brushless motor of this electric power steering apparatus is provided with an output shaft2, a rotor4with a permanent magnet3having eight magnetic poles fixedly attached to the output shaft2, a stator5arranged around the rotor4, and a rotational position sensor6arranged at an output side of the output shaft2for detecting the rotational position of the rotor4.

The stator5has twelve salient poles7arranged in opposition to the outer periphery of the permanent magnet3, insulators8attached to these salient poles7, respectively, and armature windings9of three phases U, V and W wound around the insulators8, respectively. The armature windings9have their three end portions connected with three winding terminals10, respectively, extending in an axial direction at the output side of the output shaft2.

The rotational position sensor6is composed of a resolver, and has a resolver rotor6aand a resolver stator6b. The outside diameter or contour of the resolver rotor6ais formed into a special curve so that the permeance of a diametral clearance or gap between the reservoir stator6band the resolver rotor6achanges in a sinusoidal manner at a relative angle therebetween. An excitation coil and two sets of output coils are wound around the resolver stator6b, so that a change in the diametral gap between this the resolver rotor6aand the resolver stator6bcan be detected and output from the output coils as two-phase output voltages that change in a sine curve and in a cosine curve, respectively.

The electric motor1is fixedly attached to a reduction mechanism in the form of a reduction gear11. The reduction gear11includes a gear case13to which a housing12of the electric motor1is attached, a worm gear14that is arranged in the gear case13and for decelerating the rotation of the output shaft2, and a worm wheel15that is in meshing engagement with the worm gear14. The worm gear14is formed, at an end portion thereof near the electric motor1, with a spline. A coupling16with a spline formed on its inner side is press-fitted into an end portion of the output shaft2near the reduction gear11. Thus, the coupling16and the one end portion of the worm gear14are coupled with each other through their splines, so that torque can be transmitted from the electric motor1to the reduction gear11through the coupling16.

The control unit20for controlling the driving of the electric motor1is fixedly secured to a bracket12athat is formed at an upper portion of the housing12of the electric motor1, as shown in theFIG. 2.

The control unit20includes a heat sink21that is in the shape of a box and is made of aluminum of high conductivity, a metal substrate22arranged in the heat sink21, a cover23made of aluminum that cooperates with the heat sink21to receive the metal substrate22, etc., in its interior, and a connector44.

The heat sink21, the metal substrate22and the cover23are arranged in parallel to the axial direction of the electric motor1.

FIG. 4is a cross sectional view of the metal substrate22, and the metal substrate22is composed, for instance, of an AGSP (a registered trademark of Daiwa Co., Ltd.) substrate, with a wiring pattern26abeing formed on a metal plate24made of aluminum of 2 mm thick as a copper pattern of 35 μ m through a heat dissipation insulating layer25of 80 μm. On the metal plate, four interlayer insulating layers27a,27b,27c,27deach of 60 μm thick, and four wiring patterns26b,26c,26d,26emade of copper of 35 μm thick are laminated, respectively, one over another in an alternate manner. Accordingly, the wiring patterns26athrough26ein the form of conductive layers are formed in five layers, and the wiring patterns26athrough26eare connected with one another by means of interlayer power circuit metal columns (bumps)28aand interlayer control circuit metal columns28b, respectively.

In order to raise the packaging density of parts mounted on the wiring pattern26eon the top layer thereby to make the outside dimensions of the metal substrate22small, it is preferable that no wiring pattern other than a check pattern for checking the metal substrate22after the mounting of parts be formed on the uppermost or outermost wiring pattern26e. Accordingly, it is constructed such that a majority of wiring among the parts mounted on the metal substrate22is carried out by four layers of wiring patterns26athrough26dexcepting the wiring pattern26eon the top layer.

In the metal substrate22, the uppermost insulating layer27dis formed of a material whose modulus of elasticity is smaller than those of the other insulating layers27athrough27c. The insulating layer27dwith a small modulus of elasticity serves to reduce the stress generated at soldered portions in the form of brazed portions of parts in the use environment of a motor vehicle, for example due to a temperature change between −40° C. and 125° C., thereby improving the reliability of bonding or connection of the soldered portions of the parts.

In addition, in the metal substrate22, neither any power circuit metal column body nor any control circuit metal column body is arranged in the heat dissipation insulating layer25on the metal plate24, so it is necessary for the heat dissipation insulating layer25itself to radiate heat. Thus, the heat dissipation insulating layer25is made of a material which is larger in thermal conductivity than the insulating layers27athrough27d.

On the metal substrate22, there are mounted a power main body20aat the output side of the electric motor1, and control main body20bat the opposite side thereof, as shown inFIG. 3.

The power main body20ais comprised of high current parts such as semiconductor switching elements (e.g., FET) Q1through Q6that constitutes a three-phase bridge circuit for switching a motor current of the electric motor1, capacitors30that absorb ripples of the motor current, shunt resistors31that detect the current of the electric motor1, and so on. These high current parts are mounted on the wiring pattern26ethrough soldering.

A thermal conductive sheet29having high conductivity and excellent flexibility is fitted between the upper surface of each capacitor30and the inner wall surface of the cover23.

Between the adjacent layers of the wiring patterns26athrough26earranged in opposition to heat dissipation plates (heat spreaders) hs of the semiconductor switching elements Q1through Q6, there are formed a plurality of power circuit metal column bodies on parallel lines in the thickness direction of the metal substrate22.

Since the interlayer insulating layers27a,27b,27c,27dare formed by thermally pressing a resin-coated copper foil (RCC), the power circuit metal column body between the adjacent layers of the wiring patterns26athrough26eare formed of a plurality of divided power circuit metal columns28a. The power circuit metal columns28aeach have a circular shape in cross section, so the flowability of a resin of the resin-coated copper foil can be improved, and hence internal defects or flaws of the metal substrate22can be reduced.

In this embodiment, the power circuit metal columns28aare each formed into a bump structure with a circular cross section, but a through hole structure may instead be employed which has a ring-shaped cross sectional configuration. In addition, a resin having high thermal conductivity may be filled into the hollow interior of a through hole.

The control main body20bis composed of low current parts such as a microcomputer32, a drive circuit (not shown), a peripheral circuit element including a motor current detection circuit (not shown) and so on. These low current parts are mounted on the wiring pattern26eby soldering.

The microcomputer32calculates an assist torque based on the motor current, which flows into the motor1through one end of each shunt resistor31and is detected by the motor current detection circuit (not shown), and a steering torque signal from a torque sensor (not shown), and calculates a current corresponding to the assist torque by feeding back the motor current and the rotational position of the rotor4detected by the rotational position sensor6. The microcomputer32outputs drive signals to control the semiconductor switching elements Q1through Q6of the bridge circuit.

In addition, the microcomputer32includes, though not illustrated, a well-known self-diagnosis function in addition to an AD converter, a PWM timer circuit, etc., and always carries out self-diagnosis so as to determine whether the system operates normally, so that it can interrupt the motor current upon occurrence of abnormality.

The power main body20aand the control main body20bare arranged on the single metal substrate22, and are electrically connected to one another by means of the wiring patterns26athrough26e, the interlayer power circuit metal columns28aand the interlayer control circuit metal columns28b. Accordingly, signal transmission between the control main body20band the power main body20ais carried out through the wiring patterns26athrough26e, the power circuit metal columns28aand the control circuit metal columns28bformed in the metal substrate22.

In the power main body20aincluding the high current parts such as the semiconductor switching elements Q1through Q6, the capacitors30, the shunt resistors31and so on, it is necessary for the power circuit metal columns28ato pass heat and a large current in the vicinity of the high current parts, so it is desirable that the power circuit metal columns28aeach have a cross-sectional area as large as possible.

In contrast to this, in the control main body20b, the stress generated in the soldered portions of parts due to a temperature change can be reduced, so it is desirable that the control circuit metal columns28beach have a cross-sectional area as small as possible. Therefore, the cross-sectional area of each of the power circuit metal columns28ais formed to be larger than the cross-sectional area of each of the control circuit metal columns28b. It is preferable that each of the power circuit metal columns28ahave a circular shape with a diameter of 0.7 mm or more in cross section, and that each of the control circuit metal columns28bhave a circular shape with a diameter of 0.4 mm or less in cross section.

As shown inFIG. 4, in the metal substrate22, pad portions26epare formed on the wiring pattern26eon the top layer, and a lower surface of each pad portion26epand an upper surface of the second uppermost wiring pattern26dare connected to each other by means of a corresponding control circuit metal column28b. A convex portion26fis formed on an upper surface of each pad portion26ep, and a capacitor C is mounted on adjacent convex portions26fand connected at its opposite ends with the pad portions26epby soldering. At this time, the soldering of the capacitor C is made while being lifted from the associated pad portions26epby the convex portions26f, so that solder layers are thus formed to be thick in their portions except for those portions which correspond to the convex portions26f.

Accordingly, stresses generated in the soldered portions of parts (i.e., the capacitor C) due to a temperature change in the use environment of the motor vehicle are reduced, so that the reliability of bonding or connection of the soldered portions can be improved. Here, note that the parts as referred to above may be ones of non-lead type such as resistors, etc., other than the capacitor C.

Moreover, wire bonding pad portions26eb, to which wires W made of aluminum and each having a diameter of 300 μm are wire bonded, are formed in the wiring pattern26eon the top layer of the metal substrate22, as shown inFIG. 4. The wire bonding pad portions26ebeach have a lower surface connected to an upper surface of the second uppermost wiring pattern26dby a wire metal column28c. Further, between the adjacent layers of the wiring patterns26athrough26d, there are formed wire metal columns28con a line in the thickness direction of the metal substrate22, but a wire metal column28cshould be arranged at least between the lower surface of each wire bonding pad portion26eband the upper surface of the second uppermost wiring pattern26d.

The bonding or connection of each wire W and each corresponding wire bonding pad portion26ebis made at a location excluding a portion that extends over the corresponding wire metal column28cand the interlayer insulating layer27din the lower surface of the wire bonding pad portion26eb. That is, each wire W is wire bonded to a corresponding wire bonding pad portion26ebin a region thereof in which the interlayer insulating layer27dis formed on the lower surface of the wire bonding pad portion26eb.

Alternatively, as shown inFIG. 5, each wire W is wire bonded to a corresponding wire bonding pad portion26ebin a region thereof in which a corresponding wire metal column28cis formed on the lower surface of the wire bonding pad portion26eb.

When each wire W is bonded to a corresponding wire bonding pad portion26ebwith their connecting portion or junction extending over the boundary of the corresponding wire metal column28cand the interlayer insulating layer27din the lower surface of the wire bonding pad portion26eb, the propagation of the ultrasonic wave used for wire bonding in the junction varies between a region corresponding to the wire metal column28cand a region corresponding to the interlayer insulating layer27d, thus resulting in reduced bonding or joint strength.

In addition, a metal column28cformed downward from a corresponding wire bonding pad portion26ebmay have a cross-sectional area equal to that of each power circuit metal column28a.

As shown inFIG. 3, the metal substrate22has holes22cformed therethrough at six locations in the peripheral portion thereof, and the metal substrate22is fixedly secured to the heat sink21by means of screws70threaded into these holes22c. Around each hole22c, there are arranged in a circular manner twelve fixed metal columns28d, as shown inFIG. 6, which are disposed between adjacent layers of the wiring patterns26athrough26eon individual lines in the thickness direction of the metal substrate22. Further, the fixed metal columns28dare arranged under a bearing surface of the head of each screw70, so that a force generated by tightening of the screw70is applied to the fixed metal columns28d.

In case where the metal substrate22are tightened to the heat sink21by means of the screws70through the insulating layer27dand the other interlayer insulating layers27athrough27chaving small modulus of elasticity, the screws70are easy to loose, but by tightening the metal substrate22to the heat sink21with the screws70through the fixed metal columns28d, the screws70become difficult to loose, so the metal substrate22can be made in intimate contact with the heat sink21.

Accordingly, the heat generated by heat-generating parts on the metal substrate22is efficiently conducted to the housing12of the electric motor1via the heat sink21.

Here, note that the number of fixed metal columns28dis not of course limited to twelve, but may be any value appropriate for heat conduction. Also, each of the fixed metal columns28dmay be of a cylindrical through hole structure, similar to the power circuit metal columns28a.

Although the metal plate24is made of aluminum in this embodiment, an AlSiC material may be used in which silicon carbide particles are dispersed in an aluminum material. The AlSiC material is higher in cost than aluminum but has a rigidity greater than that, so the thickness of the metal plate24can be made thinner than that of an aluminum plate, but it is preferable to select the thickness in a range substantially between 1.4 mm and 1.6 mm.

Further, the AlSiC material is smaller in the coefficient of thermal expansion than aluminum, and hence the reliability of solder bonding or joint of the parts mounted on the metal substrate22by soldering can be improved. In case where the AlSiC material is used for the metal plate24, it is preferable that an AlSiC material having a similar coefficient of thermal expansion be used for the heat sink21.

In a frame40, conductive plates41,42are insert molded in an insulating resin, with the conductive plates41being exposed from the insulating resin at portions to be electrically connected, as shown inFIG. 3. Motor terminals Mm, being formed as one ends of the conductive plates41, respectively, are protruded from corresponding holes21a, which are opening portions formed in the heat sink21, so as to be inserted into the electric motor1for electrical connection with the winding terminals10. The conductive plates41have pad portions41aformed at the other ends thereof, respectively, in a manner exposed from the insulating resin for connection to the bridge circuit of the power main body20aof the metal substrate22through wires bonded thereto by wire bonding.

The conductive plates42have pad portions42ain the form of power supply terminals formed at one ends thereof, respectively, in a manner exposed from the insulating resin, and the pad portions42aare connected to the power main body20athrough wires bonded thereto by wire bonding.

In addition, the sensor connector43is integrally formed with the frame40, and is fitted into a connector (not shown) from the rotational position sensor6. In the sensor connector43, a sensor terminal Sm for sending a signal from the rotational position sensor6to the microcomputer32is insert molded into the insulating resin.

The sensor terminal Sm has one end exposed from the insulating resin to form a pad portion Smp, and the exposed pad portion Smp is connected to the control main body20bthrough a wire bonded thereto by wire bonding.

The connector44is composed of a power connector45aelectrically connected to a battery (not shown) of the vehicle, a signal connector45bby which signals are input from and output to the vehicle side through external wiring, and a torque sensor connector46to which a signal from a torque sensor (not shown) is input. The power connector45aand the signal connector45bare integrated with each other to form a vehicle connector45, and the vehicle connector45and the torque sensor connector46are arranged in side by side.

Moreover, the connector44is composed of a connector housing47and a connector frame48received in the connector housing47, and is fixedly secured to the heat sink21at a side opposite to the metal substrate22. Further, the connector44is arranged at a side of the metal substrate22opposite to the heat sink21, and it also is arranged in the vicinity of a rear end of the electric motor1that is at a side opposite to an output side of the electric motor1.

In the connector housing47, a housing of the power connector45a, a housing of the signal connector45b, and a housing of the torque sensor connector46are integrally molded with an insulating resin.

In the connector frame48, a conductive plate49having a plus terminal49aof the power connector45aformed at one end thereof, a conductive plate50having a minus terminal50aof the power connector45aformed at the one end, a plurality of conductive plates51constituting other wiring patterns, a connector terminal52having a terminal52aof the signal connector45bformed at one end thereof, and a connector terminal53having a terminal53aof the torque sensor connector46formed at one end thereof are all insert molded into an insulating resin.

Also, in the connector frame48, exposed from the insulating resin are the plus terminal49aand the minus terminal50aof the power connector45a, the terminal52aof the signal connector45b, the terminal53aof the torque sensor connector46, the portions of the conductive plates49,50,51which are to be electrically connected, the pad portions52b,53bof the metal substrate22connected to the control main body20bthrough the wires bonded thereto by wire bonding, and so on. Thus, the vehicle connector45and the torque sensor connector46are integrally formed with the connector housing47and the connector frame48, respectively.

On the connector frame48, there are mounted, coils54,55and capacitors56that serve to prevent electromagnetic noise generated upon the switching operation of the semiconductor switching elements Q1through Q6of the power main body20afrom flowing out to the outside, and they are connected to the conductive plates49,50,51, respectively, of the connector frame48.

In addition, the connector frame48is formed with coil receiving portions48a,48b, in which the coils54,55are received and held by being inserted thereinto in a orthogonal direction with respect to the terminals49a,50a,52aof the vehicle connector45and the terminal53aof the torque sensor connector46.

FIG. 7is a cross sectional view of essential portions of the connector frame48, in which the coil receiving portion48bis formed on its bottom with a protrusion-like detent48cand a guide48dfor engagement with the coil55. The coil55is constructed by winding a conductor around a core55awhich has a T-shaped cross section when cut along an axial direction thereof. In the core55a, a large-diameter portion55bof the coil55is guided by the guide48d, so that when it is inserted up to the bottom of the coil receiving portion48b, the detent48cin the form of an engagement portion is elastically engaged with the large-diameter portion55b, thereby fixedly attaching the coil55to the connector frame48.

The terminals54a,55cof the coils54,55penetrate through holes48eformed in the bottoms of the coil receiving portions48a,48bto protrude from the connector frame48, so that they are welded and electrically connected to the conductive plates49,50,51exposed from the insulating resin.

FIG. 8is a cross sectional view of essential portions of the connector frame48, in which the connector frame48is formed with capacitor receiving portions48fthat receive the capacitors56, respectively. In the capacitor receiving portions48f, the capacitors56are arranged and received in a line or row, as shown inFIG. 3. The conductive plates49,50,51are partially exposed from the insulating resin at one end side of the capacitor receiving portions48f, and the thus exposed conductive plates49,50,51are connected to corresponding terminals of the capacitors56by TIG welding. The welded portions, being arranged on a straight line, are continuously connected by TIG welding.

The connector housing47is formed with guide portions47athat serve to guide opposite side portions48gof the connector frame48when the connector frame48is inserted into the connector housing47. In a state where the connector frame48has been completely inserted into the connector housing47, the side portions48gof the connector frame48are fitted into the guide portions47a, and the terminals49a,50a,52a,53aof the connector44and the housing of the connector44are positioned in an appropriate manner.

Moreover, in the connector44, an adhesive resin66is filled in between a terminal inserted portion, which is formed on the connector housing47and into which the terminals49a,50a,52a,53aare inserted, and a terminal protruded portion, which is formed on the connector frame48and into which the terminals49a,50a,52a,53aprotrude.

Specifically, as shown inFIG. 8, the connector frame48has a concave portion48hformed in a portion thereof into which the terminals49a,50a,52a,53aprotrude, and the connector housing47has a convex portion47bformed at an entrance portion thereof into which the terminals49a,50a,52a,53aare inserted. The adhesive resin in the form of a silicon bonding material66is filled into a gap formed between the concave portion48hand the convex portion47bwith the connector housing47being completely inserted into the connector frame48, whereby the air tightness between the terminals49a,50a,52a,53aand the connector housing47is ensured.

The heat sink21has a concave portion21cformed in a portion onto which the connector frame48is mounted, with the concave portion21cand the capacitors56being arranged in opposition to each other. The silicon bonding material66is filled into a gap between the concave portion21cof the heat sink21and the capacitors56, whereby the capacitors56are fixed to the heat sink21.

Here, note that the connector44, the heat sink21and the cover23shown inFIG. 8are kept inverted when the silicon bonding material66is filled into the gap formed between the concave portion48hand the convex portion47b, or when the silicon bonding material66is filled into the gap between the concave portion21cand the capacitors56.

Now, reference will be made to a procedure of assembling the electric power steering apparatus as constructed above.

First of all, the electric motor1is assembled in the following manner. The permanent magnet3is magnetized to eight poles by a magnetizer after fixedly bonded to the output shaft2, and an inner race of the bearing60is press-fitted over the output shaft2to form the rotor4.

Then, the armature windings9of U, V and W phases are wound around the twelve salient poles7, respectively, of the stator5through the insulators8at locations displaced at an electrical angle of 120 degrees apart from one another, so that four windings are formed for each of U, V, and W phases, thus providing a total of twelve windings. The respective U-phase winding portions have their winding-start ends and winding-termination ends connected with one another to form an entire U-phase armature winding, and the V-phase and W-phase armature windings are also formed in the same manner. After formation of the armature windings of the U, V and W phases, the winding-termination ends thereof are mutually connected with one another to provide a neutral point, whereas the winding start ends of the armature windings of the U, V and W phases are connected with the winding terminals10, respectively. Thereafter, the stator5with the windings thus formed is inserted into and fixed to the housing12.

Subsequently, after an outer race of a bearing61is fixedly attached to the housing12, the stator6bof the rotational position sensor6is fixedly attached to the housing12. Then, the output shaft2of the rotor4is inserted into an inner race of the bearing61. After a spacer62is press-fitted over the output shaft2, the output shaft2is fixed to the inner race of the bearing61. Further, the rotor6aof the rotational position sensor6and the coupling16are press-fitted over the output shaft2, and an end cover64with a rubber ring63fitted thereto is inserted into the housing12from the rear end side of the electric motor1and fixedly attached to the housing12by means of screws65.

Next, reference will be made to a procedure of assembling the control unit20.

First of all, component parts such as the semiconductor switching elements Q1through Q6, the capacitors30, the shunt resistors31, etc., which constitute the power main body20a, and component parts such as the microcomputer32, its peripheral circuit elements, etc., which constitute the control main body20b, are mounted on the metal substrate22with the individual electrodes being coated with a cream solder, and the cream solder is melted by using a reflow device, so that the above-mentioned respective component parts are soldered to the electrodes of the metal substrate22.

In addition, the capacitors56are received in the capacitor receiving portions48fof the connector frame48, and the terminals of the capacitors56are bonded by TIG welding to the conductive plates49,50,51exposed from the insulating resin.

Then, the coils54,55are inserted into coil insertion portions48a,48b, respectively. Upon insertion of the coils54,55, the terminals54a,55cpenetrate through the holes48eformed in the bottoms of the coil receiving portions48a,48bto protrude into an opposite surface of the connector frame48, so that the terminals54a,55care bonded by TIG welding to the conductive plates49,50,61exposed from the insulating resin.

Upon insertion of the coil55, the outside diameter of the large-diameter portion55bof the core55ais guided by the guide48d, and the detent48cprevents the large-diameter portion55bfrom coming off from the connector frame48in a state where the coil55has been inserted up to the bottom of the coil receiving portion48b, whereby the coil55is fixedly attached and welded to the connector frame48.

Thereafter, the connector frame48with the coils54,55and the capacitors56connected therewith is fixedly attached to the outer side of the heat sink21by means of screws67. The opposite sides of the pad portions52b,53bof the connector frame48are fixedly attached to the heat sink21by the screws67, so that the connection between the connector frame48and the heat sink21performed by wire bonding in the following step can be ensured.

The concave portion21cof the heat sink21is arranged in opposition to the capacitors56connected with the connector frame48, and the silicon bonding material66is filled into a groove21dand the concave portion21cof the heat sink21, and the concave portion48hof the connector frame48. After that, the guide portions47aof the connector housing47are inserted into the side portions48gof the connector frame48, whereby the connector housing47is fitted into the connector frame48while being guided by the guide portions47a, and is fixedly attached to the heat sink21by means of screws68.

Under such a condition, the guide portions47aand the side portions48gare fitted with each other, so the terminals49a,50a,52a,53aand the connector housing47can be positioned with respect to one another.

Moreover, the silicon bonding material66is filled into the gap formed between the concave portion48hof the connector frame48and the convex portion47bof the connector housing47, whereby the air tightness between the terminals49a,50a,52a,53aand the connector housing47can be ensured.

Further, the silicon bonding material66is filled into the gap between the concave portion21c of the heat sink21and the capacitors56, whereby the capacitors56are bonded and fixed to the heat sink21.

Then, the frame40is fitted into the heat sink21in such a manner that the motor terminals Mm and the sensor connector43are protruded from the hole21aof the heat sink21to the outside, and the frame40is fixedly secured to the inner side of the heat sink21by screws69. At this time, the frame40is fixed to the heat sink21by the three screws69that are arranged at the opposite sides of the pad portions41a, Smp and at the opposite sides of the pad portion42a.

Thereafter, the metal substrate22with parts mounted thereon is fixedly fastened to the heat sink21by the screws70. Specifically, the screws70are inserted into the holes22cformed in the metal substrate22at a total of six locations including four corners thereof and two places surrounding the power main body20a, thereby fixedly fastening the metal substrate22to the heat sink21.

After that, the pad portions41a, Smp,42aof the frame40, the pad portions52b,53bof the connector frame48, and the wire bonding pad portions26ebof the metal substrate22are electrically connected to one another through the aluminum wires W of 300 μm in diameter by means of wire bonding. Then, the cover23with a precoat gasket71coated thereon and solidified beforehand is arranged at an opening portion of the heat sink21, and fixedly fastened to the heat sink21by screws72.

Subsequently, the electric motor1and the control unit20separately assembled in the above manner are assembled with each other. A precoat gasket73is coated and solidified beforehand on the outside of the heat sink21of the control unit20, and the control unit20is fixedly attached to the bracket12aof the electric motor1by means of screws74. At this time, the mating surfaces of the electric motor1and the control unit20are sealed by the precoat gasket73.

Then, the winding terminals10of the electric motor1and the motor terminals Mm of the control unit20are fixed to each other by screws75whereby they are electrically connected with each other.

Finally, a connector (not shown) from the rotational position sensor6of the electric motor1is fitted to the sensor connector43of the control unit20to provide electrical connection therebetween, and the assembly of the electric power steering apparatus is completed.

As described in the foregoing, according to the electric power steering apparatus of this first embodiment, the power main body20aand the control main body20bare formed on the metal substrate22, and the power main body20aand the control main body20bare electrically connected to each other by the wiring patterns26athrough26eon the metal substrate22and the power circuit metal columns28aand the control circuit metal columns28b. As a result, no external connecting member connecting between the power main body20aand the control main body20bis required, so the apparatus can be reduced in size and cost, and the reliability of bonding or connection between the power main body20aand the control main body20bcan be improved.

In addition, the power circuit is constructed by electrically connecting the power main body20aand the multilayer wiring patterns26a,26b,26c,26d,26ewith one another, so the length of an electric path through which current flows is decreased, thereby making it possible to reduce electric power loss, and to suppress the generation of electromagnetic noise.

Further, between the adjacent layers of the wiring patterns26athrough26ein regions where at least semiconductor switching elements Q1through Q6are mounted on the metal substrate22, in particular in areas opposing to the heat dissipation plates (heat spreaders) hs of the semiconductor switching elements Q1through Q6, there are formed the power circuit metal columns28ain a line in the thickness direction of the metal substrate22. As a result, the heat generated by semiconductor switching elements Q1through Q6is conducted to the metal plate24in a rectilinear manner, so the heat dissipation of the metal substrate22can be improved.

Furthermore, a power circuit metal column body between the adjacent layers of the wiring patterns26athrough26eis divided into a plurality of power circuit metal columns28ahaving a circular cross section. As a result, when a resin-coated copper foil (RCC) is thermally pressed to form the interlayer insulating layers27a,27b,27c,27d, the flowability of the resin of the resin-coated copper foil is improved, so defects such as voids in the interior of the metal substrate22can be reduced, thus making it possible to improve the quality of the metal substrate22.

Still further, the cross sectional area of each of the metal columns28afor the power circuit, on which high current parts such as semiconductor switching elements Q1through Q6, etc., are mounted, is formed to be larger than the cross sectional area of each of the control circuit metal columns28bfor small current. Consequently, the heat and large current of the power main body20acan be passed through the power circuit metal columns28a, and the stress generated in the soldered portions of the low current parts of the control main body20bby a temperature change therein can be reduced, thus making it possible to improve the performance, the thermal resistance and the durability of the apparatus.

In addition, each of the power circuit metal columns28ahas a circular shape with a diameter of 0.7 mm or more in cross section, and each of the control circuit metal columns28bhas a circular shape with a diameter of 0.4 mm or less in cross section. As a result, the heat and large current of the power main body20acan be passed through the power circuit metal columns28a, and the stress generated in the soldered portions of the parts of the control main body20bby a temperature change therein can be reduced, thus making it possible to improve the performance, the thermal resistance and the durability of the apparatus.

Moreover, the metal substrate22has five layers of wiring patterns26athrough26e, and the pad portions26epare formed on the wiring pattern26eon the top layer, with a lower surface of each pad portion26epand an upper surface of the second uppermost wiring pattern26dbeing connected to each other by means of a corresponding control circuit metal column28b, so wiring for the wiring patterns is mainly made in four layers from the second uppermost layer to the lowermost or bottom fifth layer. Accordingly, wiring pattern components formed in the wiring pattern26eon the top or uppermost layer can be decreased, and hence the outside dimensions of the metal substrate22can be made smaller, thus making it possible to reduce the size of the apparatus.

Further, any wiring pattern other than the check pattern for checking the metal substrate22after the component parts has been mounted thereon is not formed in the wiring pattern26eon the top layer. Thus, the packaging density of the parts mounted on the wiring pattern26eon the top layer is raised or increased, and hence the outside dimensions of the metal substrate22can be made smaller, thus making it possible to reduce the size of the apparatus.

Furthermore, a convex portion26fis formed on an upper surface of each pad portion26ep, and a component part is mounted on this convex portion26fand soldered to the pad portion26ep. Accordingly, a solder layer can be formed thick in its portion except for that portion which corresponds to the convex portion26f, so stress generated in the soldered portion of the part due to a temperature change can be reduced, thus making it possible to improve the reliability of bonding or connection of the soldered portion.

In addition, the metal substrate22, the uppermost insulating layer27dis formed of a material whose modulus of elasticity is smaller than those of the other insulating layers27athrough27c. As a result, stress generated in the soldered portions of parts due to a temperature change can be reduced by the insulating layer27dhaving a small modulus of elasticity, so the thermal resistance and the durability of the apparatus can be improved.

Moreover, in the metal substrate22, the heat dissipation insulating layer25on the metal plate24is formed of a material that is larger in thermal conductivity than the insulating layers27athrough27d. Accordingly, the heat generated by the heat-generating parts such as the semiconductor switching elements Q1through Q6, etc., can be conducted to the metal plate24with a smaller thermal resistance, so the heat dissipation of the metal substrate22can be improved.

Further, the metal substrate22has the holes22cformed therein for fixed attachment thereof to the heat sink21, and around each hole22c, there are arranged the plurality of fixed metal columns28d, which are disposed between adjacent layers of the wiring patterns26athrough26eon individual lines in the thickness direction of the metal substrate22. Accordingly, the tightening force of a screw70, being passed through a corresponding hole22cand threaded into the heat sink21, is transmitted from the bearing surface of its head to the fixed metal columns28d, and hence there exists only the heat dissipation insulating layer25as a resin layer between the head of the screw70and the heat sink21, as a result of which the screw70becomes difficult to loose, and the metal substrate22can be made in intimate contact with the heat sink21, thus making it possible to improve the thermal resistance and the durability of the apparatus.

Furthermore, a wire bonding pad portion26eb, to which a wire W is wire bonded, is formed in the wiring pattern26eon the top layer of the metal substrate22, and the lower surface of the wire bonding pad portion26eband the upper surface of the second uppermost wiring pattern26dare connected by the wire metal columns28c. Accordingly, ultrasonic vibration generated at the time of wire bonding is effectively transmitted to a bonded portion or junction, so the reliability of bonding or connection by wire bonding can be improved.

Also, the bonding or connection of each wire W and each corresponding wire bonding pad portion26ebis made in such a manner that the wire W is wire bonded to the corresponding wire bonding pad portion26ebat a location at which the insulating layer27dis formed on the lower surface of the wire bonding pad portion26eb, or at a location in which a corresponding wire metal column28cis formed on the lower surface of the wire bonding pad portion26eb. Accordingly, the wire W and the wire bonding pad portion26ebare bonded to each other in the lower surface of the wire bonding pad portion26ebexcept for a region which extends over the metal column28cand the interlayer insulating layer27d. As a result, ultrasonic vibration generated at the time of wire bonding is effectively transmitted to a bonded portion or junction, so the reliability of bonding or connection by wire bonding can be improved.

In addition, the metal plate24of the metal substrate22is made of aluminum, and the heat sink21is similarly made of aluminum, too, so the heat generated by the heat-generating parts on the metal substrate22is efficiently conducted to the housing12of the electric motor1through the metal plate24and the heat sink21. Accordingly, the temperature rise of the heat-generating parts on the metal substrate22can be suppressed, and the thermal resistance and the durability of the apparatus can be improved. Additionally, the coefficient of linear thermal expansion of the metal substrate22and that of the heat sink21become substantially the same, so t he distances between the pad portions41a, Smp,42afixedly attached to the heat sink21and the pad portions on the metal substrate22become less prone to be changed due to a temperature change. As a result, the amount of displacement that is applied to aluminum wires connecting these pad portions is decreased, and the reliability of bonding or connection by wire bonding can be improved.

Moreover, the metal substrate22is fixedly attached to the heat sink21by means of the screws70at a total of six locations including four corners thereof and two places surrounding the power main body20a. Thus, the power main body20ais fixedly attached in the vicinity of its periphery to the heat sink21, so the heat generated by the heat-generating parts on the power main body20ais efficiently conducted to the housing12of the electric motor1through the metal plate24and the heat sink21. Accordingly, the temperature rise of the heat-generating parts on the power main body20acan be suppressed, and the thermal resistance and the durability of the apparatus can be improved.

Further, the metal substrate22is arranged in parallel to the axis of the electric motor1, and at the same time, the power main body20ais arranged at the output side of the electric motor1and the control main body20bis arranged at the opposite side thereof, so the heat generated from the power main body20ais radiated to the gear case13through the heat sink21and the bracket12aof the electric motor1. Accordingly, the temperature rise of the heat-generating parts on the metal substrate22can be suppressed, and the thermal resistance and the durability of the apparatus can be improved.

Furthermore, the power connector45a, which is electrically connected to the battery (not shown) of the vehicle, and the signal connector45b, by which signals are input from and output to the vehicle side through external wiring, are formed integrally with each other. As a result, in the case of the electric power steering apparatus being installed on the vehicle, the number of connectors required at the vehicle side becomes only one, thus making the insertion and removal work for the vehicle-side connector simple and easy.

Also, the number of connector housings and rubber packings for the vehicle-side connector can be reduced to one, so the reduction of cost can be made.

In addition, the connector44is composed of the connector frame48with the conductive plates49,50,51forming a wiring pattern being insert molded therein, and the connector housing47with the connector frame48being received therein, and these conductive plates49,50are formed at their one end with the plus terminal49aand the minus terminal50a, respectively, and the coils54,55and the capacitors56for preventing the external leakage of noise generated upon switching of the semiconductor switching elements Q1through Q6are connected to the conductive plates49,50,51. Accordingly, the length of the electric path through which current flows is decreased, thereby making it possible to reduce electric power loss, and to suppress the generation of electromagnetic noise.

Also, since the coils54,55and the capacitors56are received in the connector housing47, the reduction in size of the apparatus can be made.

Moreover, the coil55has the core55athat is formed into a T-shaped configuration in vertical cross section, and the connector frame48has the coil receiving portion48bthat is formed with the detent48cin the form of an engagement portion, and the core55ahas the T-shaped large-diameter portion55bthat is engaged with the detent48a. As a result, the coil55can be held in an appropriate manner until the terminal55cof the coil55is welded to the conductive plate51, so workability can be improved.

Further, the coils54,55are inserted into the coil receiving portions48a,48b, respectively, of the connector frame48in a direction perpendicular to the terminals49a,50aof the vehicle connector45, so that they are connected through welding with the conductive plates49,50,51. Accordingly, the length of the electric path through which current flows is decreased, thereby making it possible to reduce electric power loss, and to suppress the generation of electromagnetic noise. In addition, the coils54,55and the terminals49a,50a,52a,53aare arranged perpendicular with respect to each other, so the reduction in size of the apparatus can be made.

Furthermore, the capacitors56are received in the capacitor receiving portions48farranged in a row in the connector frame48, so the insertion of the capacitors56becomes easy, and the improvement of workability can be made.

In addition, the conductive plates49,50,51are partially exposed from the insulating resin at one end side of the capacitor receiving portions48f, and the welded portions between the exposed conductive plates49,50,51and the terminals of the capacitors56are arranged on a straight line, so the conductive plates49,50,51can be connected with the terminals of the capacitors56by means of continuous TIG welding, thus making it possible to improve workability.

Moreover, the connector housing47is formed with the guide portions47ainto which the opposite side portions48gof the connector frame48are inserted, and the guide portions47aserve as guides when the connector housing47is inserted into the connector frame48. Thus, the work of inserting the connector housing47into the connector frame48becomes easy, thereby making it possible to improve workability.

Further, the connector44is composed of the connector housing47and the connector frame48received in the connector housing47, and is fixedly secured to the heat sink21at a side opposite to the metal substrate22. As a result, the overall length of the control unit20can be shortened, and the size of the apparatus can be decreased.

Furthermore, the connector44is fixedly attached to an opposite side of the metal substrate22with the heat sink21being sandwiched therebetween. Accordingly, the dimensions or distances between the terminal52aof the signal connector45band the pad portion52bto be wire bonded, and between the terminal53aof the torque sensor connector46and the pad portion53bto be wire bonded are shortened, so the amounts of materials used by the connector terminals52,53can be decreased, and the reduction of cost can be made.

Further, the connector44is arranged in the vicinity of the rear end of electric motor1, i.e., at a side thereof opposite to its output side, so a space at the rear end of the electric motor1that is shorter than the control unit20can be effectively used, and the projected area of the apparatus when viewed from above does not increase, thus making it possible to reduce the size of the apparatus.

Furthermore, since the connector44is formed with the torque sensor connector46together with the vehicle connector45, the connectors can be collected in one place, thus contributing to the reduction in size of the apparatus.

In addition, since the torque sensor connector46is constructed of the connector housing47and the connector frame48, which are the same as those of the vehicle connector45, the number of parts can be reduced, and hence the cost and size of the apparatus can also be reduced.

Moreover, the concave portion48his formed on the connector frame48in a portion thereof into which the terminals49a,50a,52a,53aprotrude, and the convex portion47bis formed in the connector housing47at an entrance portion thereof into which the terminals49a,50a,52a,53aare inserted, so that the silicon bonding material66is filled into the gap formed between the concave portion48hand the convex portion47bwith the connector housing47being completely inserted into the connector frame48. Accordingly, the air tightness between the terminals49a,50a,52a,53aand the connector housing47can be ensured by the silicon bonding material66, and the water tightness or resistance of the apparatus can be improved.

Further, the concave portion21cis formed in a portion of the heat sink21onto which the connector frame48is mounted, and the concave portion21cand the capacitors56of the connector frame48are arranged in opposition with each other, with the silicon bonding material66being filled into the gap between the concave portion21cof the heat sink21and the capacitors56. As a result, the capacitors56are fixed to the heat sink21through the silicon bonding material66, whereby the vibration resistance of the apparatus can be improved.

Furthermore, the thermal conductive sheet29having high thermal conductivity and excellent flexibility is fitted between the upper surface of each capacitor30, which serves to absorb current ripples, and the inner surface of the cover23made of aluminum. Thus, the heat generated from the capacitors30is radiated to the cover23in addition to the metal substrate22, whereby the temperature rise of the capacitor29can be suppressed, and the durability of the capacitor29can be improved. Also, since the thermal conductive sheet29having excellent flexibility is fitted between the upper surface of each capacitor30and the inner surface of the cover23, the vibration of the upper portions of the capacitors30can be suppressed, whereby the vibration resistance of the apparatus can be improved, thus enhancing the reliability thereof.

FIG. 9is a cross sectional view showing an electric power steering apparatus according to a second embodiment of the present invention.FIG. 10is an exploded perspective view that shows a control unit20ofFIG. 9.

In this second embodiment, the housing12of the electric motor1and the heat sink21of the control unit20of the first embodiment are integrated with each other to provide a housing80. The other construction of the second embodiment is similar to that of the electric power steering apparatus of the first embodiment.

In this second embodiment, the housing80is formed with a planar portion80aat a side surface thereof that is in parallel to an axis of an electric motor1. A metal substrate22is arranged on the planar portion80a, and fixedly attached thereto by means of screws70. A frame40is also fixedly attached to the housing80by means of the screws70.

The motor terminals Mm and the sensor connector43are inserted into a hole80bformed in the housing80. The motor terminals Mm are connected with the winding terminals10, and the sensor connector43is connected with a connector (not shown) from the rotational position sensor6.

In addition, the connector44is mounted on the housing80at a side opposite to the planar portion80a, and a concave portion80dis formed in a portion of the housing80to which the connector frame48is attached. The silicon bonding material66is filled into a gap between the concave portion80dand the capacitors56connected to the connector frame48, whereby the capacitors56are fixed to the housing80.

In the assembly procedure of this second embodiment, the processes up to the assembly of the electric motor1is similar to those of the first embodiment.

The connector frame48with which the coils54,55and the capacitors56are connected is fixedly fastened by the screws67to the housing80with which the electric motor1is assembled.

Then, the silicon bonding material66is filled into a groove80eand the concave portion80dof the housing80, and into the concave portion48hof the connector frame48, respectively, and the connector housing47is fixedly attached to the housing80by means of the screws68.

Subsequently, the frame40is fixedly fastened to the housing80by means of the screws69, after which the metal substrate22with component parts mounted thereon is fixedly attached to the housing80by the screws70.

Thereafter, the pad portions41a, Smp,42aof the frame40, the pad portions52b,53bof the connector frame48, and the metal substrate22are electrically connected to one another through the aluminum wires by means of wire bonding, and a cover23with a precoat gasket71coated thereon and solidified beforehand is arranged at an opening portion of the housing80, and fixedly fastened to the housing80by screws72.

Finally, the winding terminals10of the electric motor1and the motor terminals Mm of the control unit20are fixed to each other by screws75, and a connector (not shown) from the rotational position sensor6is fitted to the sensor connector43of the control unit20to provide electrical connection therebetween, and the assembly of the electric power steering apparatus is completed.

According to the electric power steering apparatus of this second embodiment, the housing12of the electric motor1and the heat sink21of the control unit20of the first embodiment are integrated with each other to provide the housing80, so parts such as the heat sink21, the screws74, the precoat gasket73, etc., become unnecessary, and hence the number of processes for assembling these parts is reduced, thereby making it possible to reduce the manufacturing cost of the apparatus.

In addition, the bracket12aand the like, which would be necessary when the electric motor1and the control unit20are formed separately from each other, is not required, and it is also not necessary to ensure a tool space for tightening the screws74, so the reduction in size of the apparatus can be made.

Moreover, there is no impediment to obstruct thermal conduction, such as the precoat gasket73, gaps, etc., on the mounting surfaces of the electric motor1and the control unit20, so the heat generated by the heat-generating parts on the metal substrate22is conducted to the housing80of the electric motor1via the metal plate24in an effective manner. Accordingly, the temperature rise of the heat-generating parts on the metal substrate22can be suppressed, thereby making it possible to improve the thermal resistance and the durability of the apparatus.

Although in the above-mentioned embodiments, the number of magnetic poles of the permanent magnet3is eight and the number of salient poles of the stator5is twelve, the present invention is not limited to such a combination, but any combination of the number of magnetic poles and the number of salient poles may be employed for the purpose of the invention.

Further, the electric power steering apparatus is installed in an engine room, and the precoat gaskets71,73are fitted and sealed by the silicon bonding material66so as to ensure waterproofness, but the electric power steering apparatus may instead be arranged in a passenger compartment, and in such a case, the precoat gaskets71,73and the silicon bonding material66may be removed.

Furthermore, though the metal columns28a,28b,28c,28dare solid cylinders or circular columns, in case where the metal columns28a,28b,28c,28dare formed of copper by means of thick plating and etching, they become truncated cones, respectively, so the metal columns28a,28b,28c,28dmay be trapezoidal in axial cross section.

In addition, the metal plate24of the metal substrate22is made of aluminum or AlSiC material, but other metal plates such as copper may instead be used.

Moreover, although the resolver is used as the rotational position sensor6, the present invention is not limited to the use of such a resolver, but other magnetic sensing elements such as a magneto-resistive element, a Hall element, a Hall IC or the like may instead be used.

Further, the electric motor1is not limited to the brushless motor, but may be an induction motor or a switched reluctance motor (SR motor).