Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-03-16
2002-12-31
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S443000, C180S414000, C318S432000
Reexamination Certificate
active
06502024
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus in which a motor current instruction value representative of the value of the current to flow through a motor is determined based on the steering torque detected by a torque sensor and the motor is driven in accordance with the determined motor current instruction value.
An electric power steering apparatus mounted on a vehicle assists the steering power of the vehicle with a motor, and is structured so that a steering mechanism to which the steering wheel is coupled through a steering shaft is provided with a torque sensor that detects the steering torque applied to the steering wheel and a motor that assists the operation of the steering mechanism and the motor is driven in accordance with the steering torque detected by the torque sensor to thereby reduce the operation force on the steering wheel.
In a case where the steering assisting motor used in an electric power steering apparatus is, for example, a brushless motor, the brushless motor has a characteristic such that although the number of rotation increases as the applied voltage increases, the maximum value of the rotation torque determined based on the current flow is the same irrespective of the voltage as shown in
FIG. 1
, and therefore, the higher the applied voltage is, the faster the motor can rotate at the same rotation torque.
The steering assisting motor is driven by a mounted battery, and fluctuations in the voltage of the mounted battery are assumed to be, for example, 10 to 16 V. The steering assisting motor, which is designed so as to suit the assumed minimum voltage (10 V) in consideration of the fluctuations in the voltage of the mounted battery, is a low-voltage and large-current motor, and has a size larger than a motor designed for a higher voltage.
BRIEF SUMMARY OF THE INVENTION
The present invention is made in view of the above-described circumstances, and an object thereof is to provide an electric power steering apparatus in which a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery fluctuates, and the steering assisting motor can be reduced in size.
An electric power steering apparatus according to a first invention is provided with: a torque sensor for detecting a steering torque applied to a steering wheel; and a steering assisting motor driven by a drive circuit to which a voltage of a mounted battery is applied, in which a motor current instruction value representative of a value of current to flow through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor in accordance with the determined motor current instruction value, and a steering power is assisted by a rotation torque outputted by the motor, is characterized by comprising: judging means for judging whether the motor current instruction value is higher than a first threshold value or not; boosting instruction outputting means for, when the judging means judges that the motor current instruction value is higher, outputting a boosting instruction for boosting the voltage of the mounted battery; and a boosting circuit for boosting the voltage of the mounted battery in response to the boosting instruction outputted by the boosting instruction outputting means, wherein the voltage boosted by the boosting circuit is applied to the drive circuit.
In this electric power steering apparatus of the first invention, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage of the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, and the drive circuit rotates the motor based on the determined motor current instruction value. The judging means judges whether the motor current instruction value is higher than the first threshold value or not, and when the judging means judges that the motor current instruction value is higher, the boosting instruction outputting means outputs the boosting instruction for boosting the voltage of the mounted battery. The boosting circuit boosts the voltage of the mounted battery in response to the boosting instruction outputted by the boosting instruction outputting means, and the voltage boosted by the boosting circuit is applied to the drive circuit.
According to this structure, a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a second invention is characterized by further comprising in addition to the first invention: judging means for judging whether or not the motor current instruction value is lower than a second threshold value that is lower than the first threshold value during the boosting circuit boosts the voltage of the mounted battery; and stepping down instruction outputting means for, when the judging means judges that the motor current instruction value is lower, outputting a stepping down instruction for stepping down the voltage, wherein the boosting circuit stops the boosting of the voltage of the mounted battery in response to the stepping down instruction outputted by the stepping down instruction outputting means.
In this electric power steering apparatus of the second invention, during the boosting circuit boosts the voltage of the mounted battery, the judging means judges whether or not the motor current instruction value is lower than the second threshold value that is lower than the first threshold value. When the judging means judges that the motor current instruction value is lower, the stepping down instruction outputting means outputs the stepping down instruction for stepping down the voltage. The boosting circuit stops the boosting in response to the outputted stepping down instruction. According to this structure, when it becomes unnecessary to boost the voltage of the mounted battery applied to the drive circuit, the voltage can be stepped down, and when a large steering assisting force becomes unnecessary, the voltage of the mounted battery can be supplied to the steering assisting motor without boosted, so that an electric power steering apparatus is realized in which the efficiency of the steering assisting motor can be prevented from being reduced by the boosting of the voltage of the mounted battery.
An electric power steering apparatus according to a third invention is characterized by, in addition to the first invention, further comprising calculating means for calculating the rotation torque when the judging means judges that the motor current instruction value is higher; wherein the boosting instruction outputting means outputs a boosting instruction for boosting the voltage of the mounted battery to a predetermined voltage in accordance with the rotation torque calculated by the calculating means.
In this electric power steering apparatus of the third invention, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage of the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor based on the determined motor current instruction value, and the steering power is assisted by the rotation torque outputted by the motor. The judging means judges whether the motor current instruction value is higher than the first threshold value or not, and when the judging means judge
Inayama Hirohide
Ishihara Atsushi
Jonokuchi Hideki
Koyo Seiko Co. Ltd.
Nguyen Tan
Tran Dalena
LandOfFree
Electric power steering apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric power steering apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric power steering apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2970120