Electric power-steering apparatus motor apparatus

A first end region of a rotating shaft of a rotor of a brushless motor is inserted through a control apparatus housing space, and is supported by a first bearing that is held by a first bearing box that is disposed on a first surface side of a base portion of a first housing that configures the control apparatus housing space, and a second end is supported by a second bearing that is held by a second bearing box that is disposed in a motor frame that configures a motor housing space. A control apparatus is disposed inside the control apparatus housing space, and an end portion of the rotating shaft that projects out through the first bearing constitutes a coupling portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power-steering apparatus motor apparatus that is mounted to an automotive vehicle to assist steering effort by a driver, for example.

2. Description of the Related Art

Conventional pumping devices that supply oil to electric power steering apparatuses include: a heat sink is configured into a hollow shape by joining together with and fixing to a flat first member a first end surface of a second member that is formed into a vessel shape in which a first end surface is open; a motor that is mounted by joining together and fixing a motor frame to an outer surface of the first member; a pumping unit that is mounted to an outer surface of the second member; and a control unit that is joined together with and fixed to an inner surface of the second member of the heatsink where the pumping unit is disposed, and that controls driving of the motor. A first end portion of a rotating shaft of the motor is rotatably held by a first bearing that is disposed inside the motor frame, and an intermediate portion thereof is rotatably held by a second bearing that is disposed in a penetrating aperture that is formed on the first member. In addition, a second end portion of the rotating shaft projects through a penetrating aperture that is formed on the second member, and is linked to a drive shaft of the pumping unit by means of a coupling such that the pumping unit is driven by the rotating shaft of the motor and circulates oil (see Patent Literature 1, for example).

In conventional pumping devices, an inclination generally arises in a central axis of the rotating shaft that is determined by the first bearing and the second bearing relative to a central axis of the drive shaft of the pumping unit that is mounted to the outer surface of the second member due to core misalignment due to dimensional tolerances and combinations of parts, etc.

In conventional pumping devices, because the first end portion of the rotating shaft of the rotor is rotatably held by the first bearing that is disposed inside the motor frame, and the intermediate portion is rotatably held by the second bearing that is disposed on the first member, and a second end region passes through the heatsink and projects from the penetrating aperture that is formed on the second member, axial length between the second bearing and the coupling that is disposed on the second end of the rotating shaft is increased. Thus, one problem has been that vibration of the coupling is increased, increasing vibration of the pumping unit, and reducing reliability.

Because an outside diameter of the second end region of the rotating shaft that projects out through the second bearing is smaller than an inside diameter of an inner ring of the second bearing, rigidity of the second end region of the rotating shaft is reduced, and one problem has been that vibration and torque response lag arise due to torsion resonance, reducing reliability. In order to solve this problem, it is conceivable that the diameter of the second end region of the rotating shaft could be increased to increase rigidity, but in that case, it would be necessary to increase the diameter of the second bearing, giving rise to new problems such as enlargement of the device and cost increases.

Another problem has been that foreign matter may enter the heatsink through gaps between the second end region of the rotating shaft and the penetrating aperture that is disposed on the second member, giving rise to short-circuiting of the control unit, and reducing reliability.

In consideration of these conditions, conventional electric power steering apparatuses have been proposed in which a control apparatus is disposed in a space that is made by placing a first end of a first housing and a first end of a second housing in contact with each other, a motor is disposed inside a frame that is mounted to a second end of the first housing, an actuator is disposed at a second end of the second housing, a first end region of a rotating shaft of the motor is rotatably held by a first bearing that is disposed in a penetrating aperture that is formed on the second housing, a second end portion of the rotating shaft is rotatably held by a second bearing that is disposed in the frame, and a first end portion of the rotating shaft that projects out through the first bearing is linked with a drive shaft of the actuator by means of a coupling (see Patent Literature 2, for example).

In conventional electric power steering apparatuses, because the actuator is disposed at the second end of the second housing, and the drive shaft thereof is linked by means of the coupling to the first end portion of the rotating shaft of the motor that projects out through the first bearing that is disposed in the penetrating aperture that is formed on the second housing, axial length between the first bearing and the coupling that is disposed on the first end of the rotating shaft is shortened. Thus, vibration of the coupling is suppressed, reducing vibration of the actuator, and increasing reliability.

Portions of the rotating shaft between the first and second bearings are thickened, enabling rigidity of the rotating shaft to be increased without increasing the diameters of the first and second bearings, suppressing vibration and torque response lag due to torsion resonance, and enabling reliability to be increased.

In addition, because the two ends of the rotating shaft are held by the first and second bearings, foreign matter is less likely to enter the space that is made by placing the first end of the first housing and the first end of the second housing in contact with each other, suppressing occurrences of short-circuiting of the control apparatus, and increasing reliability.

In conventional electric power steering apparatuses, because the first bearing is inserted into and held by the bearing box of the second housing from a first housing side, a first bearing axial positioning wall portion of the bearing box is positioned between the first bearing and the actuator. Thus, because a distance between the first bearing and the first end of the rotating shaft is extended by a distance equivalent to the thickness of the first bearing axial positioning wall portion, one disadvantage has been that vibration of the coupling is increased, increasing vibration of the actuator, and giving rise to reductions in reliability.

SUMMARY OF THE INVENTION

The present invention aims to solve the above problems and an object of the present invention is to provide a highly reliable, compact, and low cost electric power-steering apparatus motor apparatus in which a bearing box is disposed on a first surface side of a base portion to shorten a length between a coupling portion on an axial end of a rotating shaft that projects out through a bearing that is held by the bearing box and the bearing.

In order to achieve the above object, according to one aspect of the present invention, there is provided an electric power-steering apparatus motor apparatus including: a flat base portion on a first surface side of which a first bearing box is disposed; a tubular first peripheral wall portion that is disposed on a second surface side of the base portion and that functions together with the base portion to configure a control apparatus housing space; a tubular second peripheral wall portion that is disposed on an opposite side of the first peripheral wall portion from the base portion; a floored cylindrical motor frame that is that is disposed on an opposite side of the second peripheral wall portion from the base portion so as to function together with the second peripheral wall portion to configure a motor housing space, and on a bottom portion of which a second bearing box is disposed; a motor including: a stator including: a stator core that is held inside the motor frame; and a stator winding that is mounted to the stator core; and a rotor that is disposed rotatably on an inner circumferential side of the stator such that a first end region of a rotating shaft is inserted through the control apparatus housing space and is supported by a first bearing that is held by the first bearing box, and a second end of the rotating shaft is supported by a second bearing that is held by the second bearing box, a first end of the rotating shaft that projects out through the first bearing constituting a coupling portion; and a control apparatus that is disposed inside the control apparatus housing space, and that controls driving of the motor.

According to the present invention, because a first bearing box is disposed on a first surface side of a base portion, a wall portion of the first bearing box, which positions an axial position of a first bearing, is present on a control apparatus housing space side of the base portion. Thus, a distance between a coupling portion at an axial end of the rotating shaft that projects out through the first bearing and the first bearing is shortened, suppressing vibration of the coupling portion, and thereby enabling reliability to be increased.

A portion of the rotating shaft between the first and second bearings can be thickened and rigidity of the rotating shaft increased without increasing diameters of first and second bearings, suppressing vibration and torque response lag due to torsion resonance, and enabling reliability to be increased, and also enabling size and cost reductions.

In addition, because the two ends of the rotating shaft are held by the first and second bearings, foreign matter is less likely to enter the control apparatus housing space, suppressing occurrences of short-circuiting of the control apparatus, and increasing reliability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a perspective that explains an overall configuration of an electric power steering apparatus according to Embodiment 1 of the present invention,FIG. 2is a partial cross section that explains the overall configuration of the electric power steering apparatus according to Embodiment 1 of the present invention,FIG. 3is a cross section that explains a configuration of an electric power steering apparatus motor apparatus according to Embodiment 1 of the present invention,FIG. 4is a diagram that explains a layout of power boards in the electric power steering apparatus motor apparatus according to Embodiment 1 of the present invention,FIG. 5is a diagram that explains a layout of a control board in the electric power steering apparatus motor apparatus according to Embodiment 1 of the present invention, andFIG. 6is a circuit block diagram for the electric power steering apparatus motor apparatus according to Embodiment 1 of the present invention.

InFIG. 1, an electric power-steering apparatus motor apparatus10is mounted onto a gear housing2in which a worm speed reducing mechanism1is accommodated, and is linked to a worm shaft3by means of a boss39that is described below. Torque from a rotating shaft27of a brushless motor25(described below) of the electric power-steering apparatus motor apparatus10is transmitted to the worm shaft3by means of the boss39, and is transmitted to a worm wheel4such that rotational speed of the worm shaft3is reduced. Thus, configuration is such that torque from the rotating shaft27of the brushless motor25is decelerated by the worm speed reducing mechanism1and transmitted to a column shaft5so as to assist steering effort at a steering wheel6. Torque from the column shaft5is transmitted by means of a universal joint to a pinion of a gear unit7that forms a rack-and-pinion gear mechanism, and is configured such that a rack8that intermeshes with this pinion is driven horizontally.

Next, detailed configuration of the electric power-steering apparatus motor apparatus10will be explained while referring toFIGS. 2 and 3.

An electric power-steering apparatus motor apparatus10includes: a first housing11that is mounted to the gear housing2, and that configures a control apparatus housing space100; a second housing14that is mounted to the first housing11; a motor frame15that is mounted to the second housing14, and that functions together with the second housing14to configure a motor housing space101; a brushless motor25that is disposed inside the motor housing space101; a control apparatus that is disposed inside the control apparatus housing space100, and that performs energizing control of the brushless motor25; and a rotation sensor35that detects a rotational position of a rotor26of the brushless motor25.

The first housing11is prepared by die casting an aluminum alloy, for example, and has: a flat base portion12; and a tubular first peripheral wall portion13that is disposed so as to protrude integrally from a second surface side of the base portion12. A first bearing box16is formed on a first surface side of a central portion of the base portion12. Specifically, the first bearing box16is formed on the base portion12so as to enable the first bearing17to be inserted from the first surface side of the base portion12and held. A rotation sensor positioning projection18is disposed so as to project in a cylindrical shape from the first surface of the base portion12so as to be coaxial with the first bearing box16. In addition, a first spigot portion19is disposed so as to project in a cylindrical shape from the first surface of the base portion12so as to be coaxial with the first bearing box16and so as to be radially outside the rotation sensor positioning projection18.

The second housing14, which functions as a second peripheral wall portion, is prepared so as to have a tubular shape by die casting an aluminum alloy, for example. A second spigot portion20is disposed so as to project from an end surface of the second housing14in a cylindrical shape.

The motor frame15is prepared so as to have a floored cylindrical body using iron, for example. A second bearing box21is formed on a central portion of a bottom portion of the motor frame15so as to enable the second bearing22to be inserted from inside. The motor frame15is fitted over the second spigot portion20, and is mounted to the second housing14by the fastening with a screw, for example.

The brushless motor25is a permanent-magnet synchronous motor that includes: a rotor26that has: a rotating shaft27; and a cylindrical permanent magnet28that is fitted over and fixed to the rotating shaft27; and a stator29that has: a stator core30that is prepared by laminating and integrating electromagnetic steel plates; and a three-phase stator winding31that is mounted to the stator core30so as to have a resin insulator32interposed.

The stator29is mounted to the motor frame15by press-fitting the stator core30inside the motor frame15. The rotor26is rotatably mounted such that a first end region of the rotating shaft27is inserted through the control apparatus housing space100and is supported by the first bearing17, and a second end of the rotating shaft27is supported by the second bearing22. The permanent magnet28is disposed inside the motor frame15on an inner circumferential side of the stator core30so as to ensure a predetermined air gap. The permanent magnet28is magnetized into six poles circumferentially, for example, and the three-phase stator winding31is wye-connected using motor connecting terminals34that are insert-molded into the resin terminal holder33.

The rotation sensor35includes: a resolver rotor36that functions as a sensor rotor that is fitted over and fixed to a portion of the rotating shaft27that projects through the first bearing17; and a resolver stator37that is disposed so as to surround the resolver rotor36by being positioned by the rotation sensor positioning projection18and fastened to the first surface of the base portion12by a screw (not shown), etc. Although not shown, a signal wire from the rotation sensor35is led out into the control apparatus housing space100through a penetrating aperture that has been opened through the base portion12, and is electrically connected to a control board40that is described below, and a rubber plate is disposed so as to cover the penetrating aperture, preventing entry of foreign matter to the control apparatus housing space100through the penetrating aperture. A bush38is prepared so as to have a ring body that is made of iron, and is interposed on a portion of the rotating shaft27between the first bearing17and the resolver rotor36such that an axial position of the resolver rotor36is adjusted. The boss39, which constitutes a coupling, is fixed to a coupling portion27aon a first end of the rotating shaft27.

The control apparatus has: a glass-reinforced epoxy resin control board40through which a rotating shaft insertion aperture40ais opened, and onto which electronic components such as a driver IC42a, etc., that constitute a microcomputer41and a field-effect transistor (FET) driving circuit42are mounted so as to be distributed circumferentially so as to surround the rotating shaft insertion aperture40a; ceramic power boards43to which power elements44such as power metal-oxide-semiconductor field-effect transistors (MOSFETs), etc., and semiconductor switching elements45have been mounted; and a ceramic switch board46to which semiconductor switching elements45have been mounted. A terminal portion47is a resin-molded part into which inserted conductors48are insert molded. A capacitor49that absorbs ripples in the electric current that flows to the brushless motor25, and a coil50that absorbs noise are mounted onto the terminal portion47. In addition, second ends of the semiconductor switching elements45of the switch board46are connected to a power source connector51.

As shown inFIG. 4, three power boards43that correspond to respective phases of the stator winding31are mounted to a second surface of the base portion12of the first housing11so as to be placed in close contact with the base portion12so as to be arranged in a row circumferentially at a uniform angular pitch so as to surround the first bearing box16. As shown inFIG. 4, the switch board46is mounted so as to be in close contact with the second surface of the base portion12of the first housing11. The control board40is mounted to the terminal portion47, and is disposed inside the control apparatus housing space100so as to be separated by a predetermined distance from the second surface of the base portion12such that an aperture center of the rotating shaft insertion aperture40ais aligned with a central axis of the first bearing box16. Thus, as shown inFIG. 5, the control board40is disposed so as to be perpendicular to a central axis of the rotating shaft27that is inserted through the rotating shaft insertion aperture40a, and the electronic components such as the driver IC42a, etc., that constitute the microcomputer41and the FET driving circuit42are arranged so as to be distributed circumferentially so as to surround the rotating shaft27. The control board40, the power boards43, the capacitor49, the coil50, the stator winding31, etc., are electrically connected by inserting an output terminal of the stator winding31, the inserted conductors48, etc., into a penetrating aperture40bof the control board40and soldering them to a wiring pattern (not shown) of the control board40so as to configure an electrical circuit that is shown inFIG. 6.

An electric power-steering apparatus motor apparatus10that is configured in this manner can be mounted by fitting the first spigot portion19into the gear housing2and fastening the base portion12to the gear housing2using a screw, etc. The coupling portion27aof the rotating shaft27is linked to the worm shaft3by means of the boss39. The brushless motor25can thereby be activated and controlled by the control apparatus and driven to rotate. Thus, torque from the rotating shaft27of the brushless motor25is transmitted to the worm shaft3by means of the boss39, and is decelerated by the worm speed reducing mechanism1and transmitted to a column shaft5to assist steering effort at a steering wheel6.

According to Embodiment 1, a first bearing box16is disposed on a base portion12that constitutes a first housing11and a second bearing box21is disposed on a bottom portion of a motor frame15. A rotor26is rotatably mounted such that a first end region of a rotating shaft27is inserted through a control apparatus housing space100and is supported by a first bearing17that is held by the first bearing box16, and a second end of the rotating shaft27is supported by a second bearing22that is held by the second bearing box21.

A distance between a coupling portion27aon the first end of the rotating shaft27and a first bearing17is thereby shortened. Thus, vibration of a boss39that is fixed to the coupling portion27athat results from the inclination of the rotating shaft27is reduced, suppressing vibration of a worm speed reducing mechanism1.

Thicknesses of portions of the rotating shaft27between the first bearing17and the second bearing22can also be increased without increasing the diameters of the first bearing17and the second bearing22. Thus, occurrences of the vibration and torque response lag due to torsion resonance that results from insufficient rigidity of the rotating shaft27are suppressed. In addition, the need to increase diameters of the first bearing17and the second bearing22is eliminated, enabling increases in bearing cost and increases in the size of the electric power-steering apparatus motor apparatus10to be suppressed, thereby enabling a compact, low-cost electric power-steering apparatus motor apparatus10to be achieved.

Because the first bearing box16is disposed on a first surface side of the base portion12, a wall portion of the first bearing box16that determines an axial position of the first bearing17is positioned on a control apparatus housing space100side of the first bearing17.

Thus, because a distance between the first bearing17and the coupling portion27ais shortened by an amount proportionate to the wall portion that determines the axial position of the first bearing17no longer being present between the first bearing17and the coupling portion27aof the first end of the rotating shaft27, vibration of the boss39is reduced, further suppressing the vibration of the worm speed reducing mechanism1, and enabling reliability to be improved.

Because a bush38and a resolver rotor36are fitted onto portions between the boss39of the rotating shaft27and the first bearing17, rigidity of a portion of the rotating shaft27that projects from the first bearing17can be increased without increasing the diameter of the projecting portion in question. Because resonance frequencies of the rotor26are thereby increased, vibrations that are generated due to resonance with a control period of the brushless motor25can be eliminated.

Because a resolver that has a high angular resolution is used as the rotation sensor35, rotational speed of the rotor26can be detected with high precision.

Because the resolver rotor36is mounted to the rotating shaft27in close proximity to the first bearing17, vibration of the resolver rotor36that results from vibration of the rotating shaft27can be reduced, increasing angle detecting precision by the rotation sensor35, and enabling steering feel to be improved.

Because the rotation sensor35is mounted to the base portion12and the rotating shaft27from a first surface side (a side near the worm speed reducing mechanism1) of the base portion12, the mounted angle of the rotation sensor35can be adjusted from outside, making zeroing of the resolver angle possible. The rotation sensor35is constituted by a resolver that detects angle from changes in magnetic flux, but an aluminum base portion12and an iron first bearing17are interposed between the rotation sensor35and the power boards43. Thus, magnetic effects on the power boards43and on the rotation sensor35from the power boards43due to wiring to the stator winding31are suppressed, increasing the angle detecting precision of the rotation sensor35.

Because a control board40that constitutes a control apparatus is disposed so as to be perpendicular to a central axis of the rotating shaft27, which is inserted through a rotating shaft insertion aperture40a, and electronic components such as a driver IC42a, etc., that constitute a microcomputer41and an FET driving circuit42are arranged so as to be distributed circumferentially so as to surround the rotating shaft27, cross-sectional area of the electric power-steering apparatus motor apparatus10perpendicular to the rotating shaft27can be reduced, enabling degree of freedom in mounting the apparatus to an automotive vehicle to be increased.

Because the power boards43are mounted so as to contact the base portion12, heat that is generated by the power elements44that are mounted to the power boards43is transferred to the base portion12, and is radiated from the front surface of the base portion12, enabling excessive temperature increases in the power elements44to be suppressed. Thus, the base portion12is prepared so as to have a predetermined thickness that meets requirements for heat that is generated in the power elements44to be radiated effectively. Plate thickness of the base portion12is a thickness sufficient to form first bearing box16, enabling the first bearing box16to be formed without further increasing the thickness of the base portion12.

FIG. 7is a cross section that explains a configuration of an electric power steering apparatus motor apparatus according to Embodiment 2 of the present invention.

InFIG. 7, a first housing11A is prepared by die casting an aluminum alloy, for example, and has: a flat base portion12A; and a tubular first peripheral wall portion13that is disposed so as to protrude integrally from a second surface side of the base portion12A. A first bearing box16is formed on a first surface side of a central portion of the base portion12A. A rotation sensor positioning projection18is disposed so as to project in a cylindrical shape from a second surface of the base portion12A so as to be coaxial with the first bearing box16. In addition, a first spigot portion19is disposed so as to project in a cylindrical shape from the first surface of the base portion12A so as to be coaxial with the first bearing box16.

A resolver rotor36is fitted over and fixed to a rotating shaft27in close proximity to the first bearing17, and a resolver stator37is disposed so as to surround the resolver rotor36by being positioned by the rotation sensor positioning projection18and fixed to the second surface of the base portion12A by a screw (not shown), etc. A boss39is fixed to a coupling portion27aon the first end of the rotating shaft27.

Moreover, the rest of the configuration is configured in a similar manner to Embodiment 1 above.

In an electric power-steering apparatus motor apparatus10A that is configured in this manner, because a rotation sensor35is disposed inside a control apparatus housing space100, length of projection of a rotating shaft27from a first bearing17can be shortened. Thus, a distance between the boss39and the first bearing17is further shortened, reducing vibration of the boss39that results from inclination of the rotating shaft27, and suppressing vibration of a worm speed reducing mechanism1.

Because length of a portion of the rotating shaft27that constitutes a small diameter portion that projects from the first bearing17is shortened, and portions of the rotating shaft27between the first bearing17and the second bearing22can be increased in diameter, rigidity of the rotating shaft27is increased. Because resonance frequencies of the rotor26are thereby increased, vibrations that are generated due to resonance with a control period of the brushless motor25can be eliminated.

A penetrating aperture for leading a signal wire of the rotation sensor35into the control apparatus housing space100is no longer required, preventing entry of foreign matter into the control apparatus housing space100. The signal wire of the rotation sensor35can also be electrically connected to the control board40easily.

Because the axial position of the resolver rotor36can be positioned by the rotating shaft27, a bush is no longer required, enabling configuration to be simplified and costs to be reduced proportionately.

Moreover, in each of the above embodiments, the present invention is explained as being applied to a use in which the electric power-steering apparatus motor apparatus assists steering effort on a steering wheel, but use of this electric power-steering apparatus motor apparatus is not limited to use assisting steering effort on a steering wheel, and for example, may also be applied to use driving a power steering pumping apparatus.

In each of the above embodiments, a first peripheral wall portion that functions together with a base portion to configure a control apparatus housing space is prepared integrally with the base portion, but a first housing may also be constituted only by a base portion, and a first peripheral wall portion prepared integrally with a second housing that constitutes a second peripheral wall portion.

In each of the above embodiments, power boards are constituted by ceramic circuit boards, but the power boards may also be metal circuit boards. In that case, power elements and semiconductor switching elements may be mounted to the metal circuit boards as bare chips, or discrete parts of the power elements and the semiconductor switching elements may be mounted to the metal circuit boards.

In each of the above embodiments, power elements and semiconductor switching elements are mounted to three power boards, but the power elements and semiconductor switching elements may also be mounted to a single power board.

In each of the above embodiments, the stator winding is explained as being wye-connected, but the stator winding may also be delta-connected.

In each of the above embodiments, a permanent-magnet synchronous motor is used, but the motor is not limited to a permanent-magnet synchronous motor provided that it can be used in a electric power steering apparatus, and an induction motor can be used, for example. A motor that does not use a permanent magnet is effective since magnet flux that interferes with switching of the power circuit is eliminated.

In each of the above embodiments, a rotation sensor is constituted by a resolver, but a rotation sensor that uses a Hall element may also be used, for example. In the case of a rotation sensor that uses a Hall element, because mounting space can be saved compared with a rotation sensor that uses a resolver, constraints on dimensions and shape of the circuit board when mounting the power boards are alleviated.