Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2002-12-04
2004-04-13
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C701S041000, C701S043000
Reexamination Certificate
active
06719089
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electric power steering apparatus, and more particularly to an improvement in electric power steering apparatus for motor vehicles which impart power of an electric motor to a vehicle's steering system to reduce a necessary manual steering effort of a human vehicle operator or driver.
BACKGROUND OF THE INVENTION
Various electric power steering apparatus for motor vehicles are known, in which an electric motor is driven under control of a motor controller unit, on the basis of signals output by a steering torque detector section detecting a steering torque applied to a steering wheel and a vehicle velocity detector section detecting a velocity of the vehicle, so as to reduce a necessary manual steering effort of a human operator. Among the known electric power steering apparatus is one employing a brushless motor for generating a steering torque assist.
The electric power steering apparatus employing a brushless motor can afford a stable steering assist force, because the absence of voltage drops between a brush and a commutator can prevent reduction and variation in motor output power. Further, since the brushless motor presents a smaller moment of inertia than the brush motor, the electric power steering apparatus with such a brushless motor can afford a good steering feel during high-speed straight travel or turning of a steering wheel.
However, with the electric power steering apparatus employing the brushless motor, it is necessary to control an electric current to be supplied to the motor in accordance with a current rotational angle of the motor. Thus, it has been conventional for the electric power steering apparatus to include a rotational detector section for detecting a current rotational angle of the motor and a motor-current detector section, so that the brushless motor is driven in accordance with PWM (Pulse Width Modulation) control on the basis of detection signals output from the rotational detector section and motor-current detector section.
FIG. 5
is a block diagram showing the rotor controller unit for controlling the rotation of the brushless motor. To the brushless motor
101
is connected a VR (variable Reluctance)-type resolver
102
for detecting a current rotational angle of the brushless motor
101
.
The motor controller unit
100
for controlling the rotational angle of the brushless motor
101
includes a phase correction section
103
, inertia correction section
104
and damper correction section
105
.
The phase correction section
103
of the motor controller unit
100
corrects the phase of a steering torque signal T supplied from a steering torque detector section
106
on the basis of a vehicle velocity signal v from a vehicle velocity detector section
107
, so as to output an corrected steering torque signal T′ to a target current setting section
108
. The inertia correction section
104
generates an inertia correcting signal di, on the basis of the steering torque signal T from the steering torque detector section
106
, vehicle velocity signal v from the vehicle velocity detector section
107
and angular-velocity-corresponding signal generated by a differentiation processing section
12
Id differentiating a signal corresponding to a rotational angular velocity &ohgr; of a rotor of the motor, outputs the thus-generated inertia correcting signal di to an adder section
109
. The damper correction section
105
generates a damper correcting signal dd on the basis of the steering torque signal T from the steering torque detector section
106
, vehicle velocity signal v from the vehicle velocity detector section
107
and signal corresponding to the rotational angular velocity &ohgr; of the rotor. The damper correction section
105
outputs the thus-generated damper correcting signal dd to a subtracter section
110
.
The target current setting section
108
calculates two-phase target currents Id1 and Iq1 on the basis of the corrected steering torque signal T′ output from the phase correction section
103
and vehicle velocity signal V. The target currents Id1 and Iq1 correspond to a “d” axis and “q” axis intersecting with the “d” axis on a rotational coordinate system synchronized with a rotational magnetic flux produced by a permanent magnet on the rotor of the brushless motor
101
. Hereinafter, these target currents Id1 and Iq1 will be referred to as a “d-axis target current” and “q-axis target current”, respectively.
The adder section
109
adds the d-axis target current and q-axis target current Id1 and Iq1 with the inertia correcting signal di, to thereby output inertia-corrected target currents Id2 and Iq2. The subtracter section
110
subtracts the damper correcting signal dd from the inertia-corrected target currents Id2 and Iq2, to thereby output damper-corrected target currents Id3 and Iq3. Hereinafter, these damper-corrected target currents Id3 and Iq3 will be referred to as a “final d-axis target current” Id* and “final q-axis target current” Iq*, respectively.
The final d-axis target current Id* and final q-axis target current Iq* are passed to an offset calculation section
111
, which subtracts d-axis and q-axis detected currents Id and Iq from the final d-axis and q-axis target currents Id* and Iq*, respectively, to thereby calculate offsets DId and DIq and then outputs the thus-calculated offsets DId and DIq to a PI (Proportional and Integral) setting section
112
.
The PI setting section
112
performs arithmetic operations using the offsets DId and DIq, to thereby calculate d-axis and q-axis target voltages Vd and Vq such that the d-axis and q-axis detected currents Id and Iq follow the final d-axis target current Id* and final q-axis target current Iq*, respectively. The d-axis and q-axis target voltages Vd and Vq are corrected, via an interference-preventing control section
113
and arithmetic section
114
, to d-axis and q-axis corrected target voltages Vd′ and Vd′ that are then delivered to a dq-to-three-phase conversion section
115
.
Only one set of the adder section
109
, subtracter section
110
, offset calculation section
111
, PI setting section
112
and arithmetic section
114
are shown in
FIG. 5
for purposes of clarity; in practice, however, two separate sets of these sections
109
,
110
,
111
,
112
and
114
are provided for the two target currents Id1 and Iq1.
The interference-preventing control section
113
calculates interference-preventing control correction values for the d-axis and q-axis target voltages Vd and Vq, on the basis of the d-axis and q-axis detected currents Id and Iq and rotational angular velocity &ohgr; of the rotor.
The arithmetic section
114
subtracts the respective interference-preventing control correction values from the d-axis and q-axis target voltages Vd and Vq, to thereby calculate d-axis and q-axis corrected target voltages Vd′ and Vq′ that are output to the dq-to-three-phase conversion section
115
.
The dq-to-three-phase conversion section
115
converts the d-axis and q-axis corrected target voltages Vd′ and Vq′ to three-phase target voltages Vu*, Vv* and Vw* and outputs the thus-converted three-phase target voltages Vu*, Vv* and Vw* to a motor drive section
116
.
The motor drive section
116
includes a PWM-controlled voltage generation section and inverter circuit (both not shown). The motor drive section
116
generates, by means of the not-shown PWM-controlled voltage generation section, PWM-controlled voltage signals UU, VU and WU corresponding to the three-phase target voltages Vu*, Vv* and Vw*, and it outputs these PWM-controlled voltage signals UU, VU and WU to the not-shown inverter circuit. Then, the inverter circuit generates three-phase A.C. driving currents Iu, Iv and Iw corresponding to the PWM-controlled voltage signals UU, VU and WU, which are supplied via three-phase driving current paths
117
to the brushless motor
101
. The three-phase A.C. driving currents Iu, Iv and Iw are each a sine-wave current for driving the brus
Kuribayashi Takashi
Shimizu Yasuo
Takagi Masanori
Yoneda Atsuhiko
Lum L.
Merchant & Gould P.C.
Morris Lesley D.
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