JP2003267234A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturizable electric power steering device requiring no reduction gear with a large reduction ratio. <P>SOLUTION: This electric power steering device calculates torque applied to steering shafts 22 and 24 based on the difference in the rotation angles at locations of different longitudinal direction of the steering shafts 22 and 24, which connects a steering wheel 20 of a car to a steering mechanism of wheels (not shown in Fig.), and drives and controls a motor 4 installed to the steering mechanism or a steering shaft 24 to support steering, in order to apply additional force to the steering mechanism according to the direction and amount of calculated torque. The motor 4 is a vernier motor. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a torque applied to a steering shaft of a vehicle for steering, and provides a steering assist motor based on the detected torque. The present invention relates to an electric power steering device that performs drive control. 2. Description of the Related Art A steering assist motor is driven based on a detection result of a torque applied to a steering wheel (steering wheel) for steering operation, and the torque of the motor is transmitted to a steering mechanism to perform steering. The assisted electric power steering device controls the assist force characteristics according to the traveling state, such as the speed of the vehicle, the frequency of the steering, and the like, as compared with the hydraulic power steering device using the hydraulic actuator as the source of the steering assist force. Has an advantage that the application range is easy, and in recent years, its application range tends to be expanded. [0003] The electric power steering apparatus is a column assist type, depending on a position where a motor for steering assist is mounted.
A brush motor or a SPM (Surface Permanent Magnet) brushless motor is used as a motor to be used in any of the rack assist type and the pinion assist type.
or Permanent Magnet) Application of brushless motors is also being considered. However, all of the above motors have a small rated torque, so that when used in an electric power steering apparatus, a large reduction ratio is required to obtain a sufficient steering assist force. A reduction gear is required, and as a result, there is a problem that the size of the electric power steering device cannot be reduced. The present invention has been made in view of the above-described circumstances, and has as its object to provide an electric power steering device that does not require a reduction gear having a large reduction ratio and that can be reduced in size. [0005] An electric power steering apparatus according to the present invention provides a steering shaft for connecting a steering member of a vehicle and a wheel-side steering mechanism at different rotational angles in an axial direction. Calculating a torque applied to the steering shaft based on the difference between the steering shaft and the steering shaft provided on the steering mechanism or the steering shaft in order to apply an assisting force corresponding to the calculated direction and magnitude of the torque to the steering mechanism. In an electric power steering apparatus for controlling the driving of an auxiliary motor, the motor is a vernier motor. In this electric power steering apparatus, a torque applied to the steering shaft is calculated, and an assisting force corresponding to the direction and magnitude of the torque is applied to the steering mechanism or the steering shaft. The drive of the steering assist motor is controlled. The steering assist motor is a vernier motor. The conventional synchronous motor rotates at the same rotation speed as the rotating magnetic field, whereas the vernier motor rotates at a lower rotation speed than the rotating magnetic field by a fixed ratio, so that it rotates at low speed and can output a large torque. Therefore, a reduction gear having a large reduction ratio is not required, and an electric power steering device that can be downsized can be realized. Hereinafter, the present invention will be described with reference to the drawings showing an embodiment thereof. FIG. 1 is a block diagram showing a main configuration of an electric power steering apparatus according to an embodiment of the present invention. In this electric power steering apparatus, a torque detection signal detected and output by a torque sensor 1 that detects a torque applied to a steering shaft (not shown) includes:
The torque signal processed by the arithmetic processing circuit 9 and generated by the arithmetic processing circuit 9 and the vehicle speed signal detected and output by the vehicle speed sensor 7 for detecting the speed of the vehicle are provided to the control unit 2. [0008] A relay control signal output from the control unit 2 is input to the relay drive circuit 5, and the relay drive circuit 5 turns on or off the fail-safe relay contact 5a according to the relay control signal. The control unit 2 creates a motor current target value by referring to a torque / current table 8a in the built-in assist control unit 8 based on a torque signal, a vehicle speed signal, and a motor current signal described later. The control unit 2 provides the motor drive circuit 3 with the created motor current target value as an output level instruction signal and a rotation direction instruction signal. The motor drive circuit 3 receives the power supply voltage of the vehicle-mounted battery P through the fail-safe relay contact 5a, and rotationally drives the steering assist motor 4, which is a vernier motor, based on the given output level instruction signal and rotation direction instruction signal. Let it. The motor current flowing through the steering assist motor 4 is detected by the motor current detection circuit 7 and is provided to the control unit 2 as a motor current signal, and is used for feedback control of the motor current. FIG. 2 is a partial cross-sectional view showing an example of the structure of the vernier motor. Vernier motor, PM type, SP
As shown in FIG. 2A, the PM type is provided on the teeth 12 side of the stator 11 as well.
The magnets 15 are arranged at equal intervals at positions opposite to each other, and the magnets 1 are arranged at equal intervals on the rotor 13 side.
The magnets 4 and the teeth 15 on the teeth 12 side are magnetized to the same polarity on the side facing the air gap, and have different polarities on the rotor 13 side and the teeth 12 side. It is desirable that the teeth 12 of the stator 11 and the opening of the slot 16 (the magnet portion formed by the coil 10) have substantially the same width. In the PM type vernier motor, the stator 1
The number of slots 16 in one slot is Z1, the number of slots in rotor 13 is Z2, and the rotor 13
Side magnet 14 and teeth 12 side magnet 1
Assuming that the number of winding pole pairs representing the number of locations where 5 strongly attracts is p, the relational expression of Z2 = Z1 ± p holds. For example, U
The U 'phase is determined for each phase, and U-U' determines the number of winding pole pairs p.
Is defined as 1. The coil 10 is distributed-wound. For example, the slot 16 corresponding to the slot 16 at θ = 0 is the slot 16 at θ = 180 ° / p. That is, the winding for one pole pair is performed between the slot 16 at θ = 0 and the slot 16 at θ = 180 ° / p. In the SPM type, as shown in FIG. 2B, magnets 14a are arranged near the surface of the rotor 13a at equal intervals with alternate magnetic poles. The teeth 12a of the stator 11a and the opening of the slot 16a (the magnet portion formed by the coil 10a) do not need to have the same width. The number of teeth 12a of the stator 11a must be a multiple of six. In the SPM type vernier motor, the number of slots 16a of the stator 11a is Z1, the number of pole pairs of the rotor 13a is Z2, and the number of large magnetic circuits formed through the back yoke of the stator 11a when no power is supplied is divided by 2. Assuming that the number of pairs of winding poles representing the object is p, a relational expression of Z2 = Z1 ± p holds as in the SPM type. Other structures are the same as those of the SPM brushless motor. In the vernier motor, a secondary component of a gap permeance (reciprocal of reluctance (magnetic reluctance)) distribution, which is rotated by rotation of the rotors 13 and 13a, has a rotating magnetic field generated by a three-phase winding of the stators 11 and 11a. By rotating synchronously, reluctance torque is generated,
The rotors 13 and 13a rotate. The rotation speed of the rotors 13 and 13a is p / Z2 of the rotation speed of the rotating magnetic field. However,
p and Z2 are the numerical values described above. FIG. 3 shows a steering assisting motor 4 which is a PM type or SPM type vernier motor, and a motor driving circuit 3.
FIG. 3 is a block diagram showing a configuration of the drive circuit included in the configuration. The vernier motor 4 includes a stator 4a in which coils A, B, and C are star-connected, and a rotor (rotor) 4b that is rotated by a rotating magnetic field generated by the coils A, B, and C. Switching circuit 3b of motor drive circuit 3
The transistors Q1 and Q2 connected in series and the diodes D1 and D2 connected in series in the opposite direction are connected in parallel between the DC power supply terminal and the ground terminal, and the transistors Q3 and Q4 are connected in series. Diodes D3 and D4 connected in series in the reverse direction are connected in parallel, and transistors Q5 and Q6 connected in series and diodes D5 and D6 connected in series in the reverse direction are connected in parallel. The other terminal U of the star-connected coil A is connected to the common connection node of the transistors Q1 and Q2 and the common connection node of the diodes D1 and D2. Diode D
The other terminal V of the star-connected coil B is connected to the common connection node of the transistors Q5 and Q4.
6 and the common connection node of the diodes D5 and D6 are connected to the other terminal W of the star-connected coil C.
Is connected. The gate control circuit 3c is supplied with an instruction signal of a rotation direction and an output level from the control unit 2. The gate control circuit 3c turns on / off the gates of the transistors Q1 to Q6 according to the instruction of the rotation direction and the rotation position of the rotor 4b, for example, UV, UW, VW, V −
As in U, WU, WV, and UV, the path of the current flowing through the stator 4a is switched to generate a three-phase rotating magnetic field. The current value as the output level is determined by transistors Q1 to Q
6 is controlled to increase or decrease by PWM (Pulse Width Modulation) control. Diodes D1 to D6
Is for absorbing noise generated by turning on / off the transistors Q1 to Q6. FIG. 4 is a sectional view showing the structure of the electric power steering apparatus according to the present invention. This electric power steering device includes an input shaft 22 connected to a steered wheel 20.
And an output shaft 24 coaxially connected to the input shaft 22 via a torsion bar 19, and a torque applied to the input shaft 22 by rotating the steered wheels 20.
A torque sensor 1 for detecting a torsion caused by the torque sensor 1, an arithmetic processing circuit 9 for arithmetically processing a torque detection signal detected and output by the torque sensor 1, and outputting a torque signal;
Has a vernier motor 4 that is driven through a motor drive circuit 3 based on the torque signal output by the arithmetic processing circuit 9, and rotates the vernier motor 4 through an output shaft 24 and an output shaft 24 through a reduction gear mechanism 27. Is transmitted to a steering mechanism (not shown) via transmission means connected to the steering mechanism. Since the vernier motor 4 outputs a large torque, the reduction gear mechanism 27 can reduce the reduction ratio and reduce the size. The input shaft 22 has a cylindrical portion 22a into which one end of the torsion bar 19 is inserted, and one end of the cylindrical portion 22a is rotatably supported in the housing 30 via a needle bearing 29. The output shaft 24 is formed in a cylindrical shape into which the other end of the cylindrical portion 22a and the other end of the torsion bar 19 are inserted. One end of the output shaft 24 is rotatably supported in the housing 30 via rolling bearings 32 and 33 in the middle in the axial direction. In this embodiment, the column assist type electric power steering device has been described. However, it is needless to say that the vernier motor 4 can be similarly applied to the rack assist type and the pinion assist type electric power steering device. . Disclosure technology. FIG. 5 is a longitudinal sectional view showing the structure of the slotless motor disclosed this time. This slotless motor is provided along a rotor shaft 40 supported by a housing 44 via a bearing, a rotor core 43 fixed to the rotor shaft 40, and an inner peripheral surface of the housing 44, and is made of a laminated steel plate. The stator core 41 is fixed with a stator yoke 41 on the inner peripheral surface of the stator yoke 41.
Air-core coil 4 mounted with an air gap separated from 3
2 is provided. The coil 42 is formed by winding a litz wire (twisted wire) as shown in FIG. 6. The litz wire is formed by twisting, for example, seven enamel wires 45, and the outer periphery thereof is made of a material that is easily melted such as an esterimide 46. Coated with In a slotless motor, the winding is air-core and the winding inductance is small. Therefore, in order to achieve high efficiency and low torque ripple, it is necessary to increase the frequency of the inverter. However, due to the skin effect, the winding resistance increases in a high frequency region, and a large loss occurs. Therefore, it has been difficult to apply the slotless motor to the electric power steering device. However, as described above, the coil 4
The use of a litz wire for 2 reduces the skin effect, reduces the increase in AC resistance due to high frequency, and suppresses the temperature rise of the coil, so that a slotless motor can be applied to an electric power steering device. It becomes possible. Here, the relationship between the diameter of the enameled wire 45 and the loss will be considered. Consider a case where a high-frequency current of 100 [kHz] flows. The resistance R _{0 at} the direct current of the conductor,
In considering the ratio between the effective resistance R and the reactance X, a parameter u is used as shown below. u = r (μσω) ^1/2 r; diameter of conductor [m], μ; permeability of conductor [H / m] σ; conductivity of conductor [Ω ^-1 / m], ω; angular frequency [rad]
/ Sec] When the conductor is copper, vacuum permeability μ ₀ = 4π × 10 ⁻⁷ [H / m] Copper permeability μ = pμ ₀ = μ ₀ (∵specific permeability p = 1) Copper conductivity Degree σ = 58 × 10 ^{6 It} is assumed that one single wire having a diameter of 1.25 [mm] is used as a coil winding. At this time, u = 3.375 From the graph showing the relationship between the effective resistance and the reactance of the cylindrical conductor in FIG. 7, R / R ₀ = 1.45 and X / R ₀ = 1.
The DC resistance becomes 2.55 times as a sum of the two. Therefore, instead of a single wire, the diameter is 0.47.
As shown in FIG. 6, seven enamel wires of [mm] are used. (The cross-sectional area of a single wire having a diameter of 1.25 [mm] is substantially equal to the cross-sectional area of seven single wires having a diameter of 0.47 [mm].) In this case, u = 1.27. From the graph of FIG. 7, it can be seen that the DC resistance becomes 1.2 times when the DC resistance is similarly obtained. Considering that the DC resistance when using a single wire having a diameter of 1.25 [mm] is 2.55 times, the diameter is 0.47 [m].
m], the DC resistance of the seven litz wires of the enameled wire is greatly reduced. Therefore, when the above-mentioned litz wire is applied to a coil of a slotless motor, an increase in DC resistance when a high-frequency current flows can be suppressed, and the loss in the coil is less than half that of a single wire. become. Also, coating with an esterimide facilitates soldering and enhances the insulating effect. According to the electric power steering apparatus of the first invention, it is possible to realize an electric power steering apparatus which does not require a reduction gear having a large reduction ratio and can be downsized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a main configuration of an embodiment of an electric power steering device according to the present invention. FIG. 2 is a partial cross-sectional view showing a structural example of a vernier motor. FIG. 3 is a block diagram illustrating a configuration of a steering assist motor that is a PM type or SPM type vernier motor and a drive circuit included in the motor drive circuit. FIG. 4 is a sectional view showing a configuration of an electric power steering device according to the present invention. FIG. 5 is a longitudinal sectional view showing the structure of the slotless motor disclosed this time. FIG. 6 is a sectional view showing a section of a litz wire. FIG. 7 is a graph showing a relationship between an effective resistance and a reactance of a cylindrical conductor. [Description of Signs] 1 Torque sensor 2 Controller 3 Motor drive circuit 4 Motor for assisting steering (Vernier motor) 4a Stator (stator) 4b Rotor (rotor) 10 Coil 11, 11a Stator 12, 12a Teeth 13, 13a Rotors 14, 14a, 15 Magnets 16, 16a Slot 19 Torsion bar 20 Steering wheel 22 Input shaft 24 Output shaft 27 Reduction gear mechanism

Claims (1)

Claims: 1. A torque applied to a steering shaft that connects a steering member of a vehicle and a steering mechanism on a wheel side based on a difference in rotation angle between different positions in an axial direction of the steering shaft. And an electric power steering that drives and controls a steering assist motor provided on the steering mechanism or the steering shaft in order to apply an assisting force corresponding to the calculated direction and magnitude of the torque to the steering mechanism. In the apparatus, the motor is a vernier motor.