Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1998-08-07
2001-07-17
Schwartz, Christopher P. (Department: 3613)
Motor vehicles
Steering gear
With electric power assist
Reexamination Certificate
active
06260655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electric power steering apparatuses for automotive vehicles which provide output power of an electric motor to the vehicle steering system to reduce a steering effort to be manually applied by a vehicle driver. More particularly, the invention relates to an electric power steering apparatus which is capable of determining an actual winding resistance value of the electric assisting motor through arithmetic operations.
2. Description of the Related Art
Electric power steering apparatuses are widely used today in automotive vehicles. Improved electric power steering apparatuses have been known, which are arranged to constantly detect a rotating speed of the electric assisting motor and execute so-called “unload control” to decrease a target motor current when the detected rotating speed of the motor is below a predetermined value, (i.e., the motor is in a virtually stationary or nonrotating condition) and a current actually flowing through the motor is over a predetermined value, so as to avoid a waste of the current flowing through the motor.
Whereas a rotating speed sensor, typically in the form of a tacho-generator, is generally used to detect the motor rotating speed (M
V
), some of the electric power steering apparatuses, rather than using such a sensor, determine the motor rotating speed (M
V
) from following Equation (1) using a winding resistance value of the motor (R
M
), current actually flowing through the motor (I
M
) and voltage supplied to the motor (V
M
):
M
V
=V
M
−R
M
×I
M
Equation (1)
However, because the winding resistance value R
M
applied to Equation (1) is a fixed value as specified in the specifications of the motor, the motor rotating speed M
V
often can not be calculated accurately from Equation (1) if an actual winding resistance value R
M
of the motor in operation substantially differs from the specified fixed value. Thus, where the motor rotating speed M
V
calculated on the basis of the fixed winding resistance value R
M
is used for the unload control, the assisting motor would rotate at different speeds than those actually required, with the result that proper unload control is not achieved.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electric power steering apparatus which is capable of calculating an actual winding resistance value of an electric assisting motor employed with high accuracy, to thereby permit proper unload control and hence good steering control.
According to a first aspect of the present invention, there is provided an electric power steering apparatus for an automotive vehicle, which comprises: an electric motor for applying an electric steering assist to a steering system interconnecting a steering wheel and steered wheels of the automotive vehicle; a steering torque sensor for detecting steering torque applied to the steering system; a motor voltage detector for detecting a motor voltage supplied to the electric motor; a motor current detector for detecting a motor current flowing through the electric motor; a motor condition detector for detecting a zero-rotating-speed condition of the electric motor; a control unit including a current setting section for setting a target motor current corresponding at least to the steering torque detected by the steering torque sensor, a drive control section for generating a motor control signal on the basis of an offset between the target motor current and the motor current detected by the motor current detector, and a motor resistance calculating section for, on the basis of the motor voltage and motor current, calculating a winding resistance value of the electric motor when the motor condition detector is detecting the zero-rotating-speed condition of the electric motor; and a motor drive for driving the electric motor on the basis of the motor control signal generated by the drive control section.
The control unit further includes a comparator section for making a comparison between a steering angle detected by the steering angle sensor and a reference steering angle corresponding to the zero-rotating-speed condition of the electric motor. When a result of the comparison by the comparator section indicates that the steering angle detected by the steering angle sensor is greater than the reference steering angle, the motor resistance calculating section executes a division of the motor voltage detected by the motor voltage detector by the motor current detected by the motor current detector, to thereby calculate the winding resistance value. When, however, the motor current detected by the motor current detector is below a predetermined value, the motor resistance calculating section does not execute the division.
By the inclusion of the motor condition detector for detecting a zero-rotating-speed condition of the electric motor and the motor resistance calculating section for calculating the winding resistance value of the electric motor on the basis of the motor voltage and motor current, the electric power steering apparatus according to the first aspect can accurately determine an actual winding resistance value of the motor, being employed in the apparatus, when the vehicle steering system is in a rack-end state and the rotating speed of the motor is zero.
According to a second aspect of the present invention, there is provided an electric power steering apparatus for an automotive vehicle, which comprises: an electric motor for applying an electric steering assist to a steering system interconnecting a steering wheel and steered wheels of the automotive vehicle; a steering torque sensor for detecting steering torque applied to the steering system; a motor voltage detector for detecting a motor voltage supplied to the electric motor; a motor current detector for detecting a motor current flowing through the electric motor; a control unit including a current setting section for setting a target motor current corresponding at least to the steering torque detected by the steering torque sensor, a drive control section for generating a motor control signal on the basis of an offset between the target motor current and the motor current detected by the motor current detector, a comparator section for making a comparison between the motor current detected by the motor current detector and a maximum target motor current set by the current setting section, and a motor resistance calculating section for calculating a winding resistance value of the electric motor when the motor current detected by the motor current detector has become greater the maximum target motor current; and a motor drive for driving the electric motor on the basis of the motor control signal generated by the drive control section.
By the inclusion of the comparator section for making a comparison between the motor current detected by the motor current detector and a maximum target motor current set by the current setting section and the motor resistance calculating section for calculating a winding resistance value of the electric motor when the motor current detected by the motor current detector has become greater the maximum target motor current, the electric power steering apparatus according to the second aspect can determine the actual winding resistance value of the electric assisting motor being employed in the apparatus, by detecting a point when the motor current has exceeded the maximum target motor current value and treating the detected point as a zero-rotating-speed condition of the assisting motor. This arrangement can eliminate a need for the above-mentioned motor condition detector.
REFERENCES:
patent: 5631833 (1997-05-01), Wada
patent: 5984042 (1999-11-01), Nishimoto
patent: 5992558 (1999-11-01), Noro
patent: 6008599 (1999-12-01), Beck
Mukai Yoshinobu
Noro Yoshiki
Bartz C. T.
Honda Giken Kogyo Kabushiki Kaisha
Merchant & Gould P.C.
Schwartz Christopher P.
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