Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Electric vehicle
Reexamination Certificate
2002-02-19
2003-11-11
Zanelli, Michael J. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Electric vehicle
C180S065100, C180S065800
Reexamination Certificate
active
06647325
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention pertains to a control system of controlling an electric motor used for a drive unit for an electric vehicle such as an electric scooter, an electric car or the likes.
BACKGROUND OF THE INVENTION
In general, an electric motor comprises a rotor having a field system and a stator having n phases armature coils (n is two or more integers) and is adapted to control a rotational speed by controlling a drive current flowing through the armature coils by means of a controller. Of late, there has been used one having a microprocessor provided as the controller.
In many cases, a brushless DC motor has been used for the electric motor driving the electric vehicle. As well known, the brushless DC motor comprises a rotor having a magnet field system and a stator having armature coils of multi-phases such as two or more phases. The rotor is rotated by switching an exciting phase of the armature coils to selectively energize the armature coils in accordance with a rotational angle position of the rotor relative to the stator.
A drive unit for driving the motor comprises position sensors to detect a rotational angle position of the rotor relative to the stator, a switch circuit to switch the exciting phase of the armature coils, an accelerator operation member operated when an output of the motor should be adjusted, an acceleration sensor to output an acceleration signal having a magnitude corresponding to the opening degree of the accelerator operation member which is detected as a displacement quantity of the accelerator operation member and a controller to control the switch circuit so that the armature coils are selectively energized to commutate in accordance with the output of the position sensors which flow through the armature coils to rotate the rotor.
The controller comprises a microprocessor to perform a predetermined program, which forms duty factor arithmetical operation means to arithmetically operate a duty factor of the drive current on a value of the acceleration signal, PWM control means to control the switch circuit so as to modulate a waveform of the drive signal into a pulse width modulation waveform (PWM waveform) having the duty factor DF arithmetically operated by the duty factor arithmetical operation means and current phase angle control means to shift the switching angle of the exciting phase of the armature coils by an advance angle relative to a reference switching angle determined on the output of the position sensors.
The duty factor DF of the drive current shows the ratio of an on-time of the drive current relative to the on-off period thereof and is determined by (t on/T)×100[%] wherein “t on” designates a time during which the drive current flows, “t off” designates a time during which the value of the drive current is zero and “T” (=t on+t off) designates an on-off period.
In the electric vehicle, there is adjusted the output of the electric motor by displacing the accelerator operation member such as an accelerator grip or an accelerator pedal and, in order to obtain a good operation feeling of the vehicle and a smooth operation thereof, the duty factor DF of the drive current should be controlled relative to both of the displacement quantity (the opening degree &agr; of the accelerator) and the rotational speed N of the motor whereby the change rate of the duty factor DF relative to the accelerator operation member varies in accordance with the rotational speed [rpm].
In the case where the duty factor DF is controlled relative to both of the opening degree &agr; of the accelerator and the rotational speed N of the motor, a three-dimensional look-up table giving a relationship between the opening degree &agr; of the accelerator, the rotational speed N of the motor and the duty factor DF of the drive current is stored in a ROM, the duty factor DF is arithmetically operated on the rotational speed N of the motor and the opening degree &agr; of the accelerator by the microprocessor with this look-up table used and switch elements of the switch circuit are controlled so that the drive current intermittently flows in the thus obtained duty factor DF.
In the brushless DC motor, the actual switching angle (the electrical angle) for switching over the exciting phase of the armature coils is shifted just by the predetermined angle relative to a theoretical switching angle determined by the mechanical structure of the electric motor. A phase difference between the actual switching angle and the theoretical switching angle is called a current phase angle &ggr;, which is generally set on an advance side.
The generation torque and the maximum rotational speed of the brushless DC motor vary on the current phase angle &ggr;. As the current phase angle &ggr; is so set that the torque is larger, the maximum rotational speed gets lower and as the current phase angle &ggr; is advanced, the maximum rotational speed gets higher, but the generation torque gets lower.
Generally, in the case where the brushless DC motor is used as the drive unit of the electric vehicle, the current phase angle &ggr; by which the fully high torque can be obtained at the low speed is set as a regular current phase angle &ggr;o, the current phase angle &ggr; is advanced relative to the regular current phase angle &ggr;o as the rotational speed increases in the area where the rotational speed exceeds the set value, and the advance amount of the current phase angle &ggr; is held at the maximum value in the area where the rotational speed exceeds the set advance termination rotational speed at which the advance of the current phase angle is terminated.
In the case where the aforementioned control of the current phase angle is performed, a three-dimensional look-up table giving a relationship between the displacement quantity &agr; of the accelerator operation member (the opening degree of the accelerator), the rotational speed N of the motor and the current phase angle &ggr; is stored in the ROM, the current phase angle &ggr; is arithmetically operated on the detected value of the opening degree of the accelerator and the detected value of the rotational speed by using the look-up table and the current phase angle of the electric motor is controlled so as to be equal to the arithmetically operated current phase angle.
In the case where the current phase angle &ggr; is advanced more than the regular current phase angle &ggr;o in the area where the rotational speed exceeds the set value as aforementioned, when the vehicle is running uphill in the full accelerating state where the accelerator operation member is displaced to the maximum value toward the accelerating side, the advance quantity of the current phase angle is held at the maximum value and therefore the drive current of the electric motor exceeds the rated value. As this state continues for a long time, the temperature of the armature coil rises and sometimes exceeds the allowable value. Especially, as the rotational speed of the electric motor is extremely lowered on the uphill road, it takes longer for the drive current to be commuted so that the temperature of the specific phase armature coil of the electric motor abruptly rises and therefore it is possible that the armature coil is damaged by heat. As the lock state where the electric motor stops rotating on the uphill road arises, the temperature of the armature coil of the specific phase determined on the stop position of the rotor rises and the armature coil is therefore damaged by heat because the large drive current flows through the specific phase armature coil.
Thus, the prior control system for the brushless DC motor for the electric vehicle is provided with a temperature sensor to detect the temperature of the armature coils, and when it is detected by the temperature sensor that the temperature of the armature coils abnormally rises, the drive current is limited so as to restrict the output of the electric motor whereby the temperature of the armature coils is prevented from rising.
However, if
Inaba Yutaka
Shimazaki Mitsuyoshi
Gibson Eric
Kokusan Denki Co. Ltd.
Pearne & Gordon LLP
Zanelli Michael J.
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