Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Reexamination Certificate
2000-02-24
2001-11-27
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
C361S087000, C361S093900
Reexamination Certificate
active
06324038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a motor protecting apparatus, and in particular to a current supply control apparatus having an overcurrent protective function of protecting an electrically-powered motor and a drive control circuit therefor with suppression of overcurrent in an electric vehicle.
2. Description of the Prior Art
In recent years, engineers rapidly pursue development of electrically-powered motor vehicles, and particularly demand for electric cars including hybrid cars is rapidly increased for the purpose of environmental protection measures. Either a DC motor or an AC motor is used as a driving power unit of this type of electric vehicles. In particular, a synchronous motor using permanent magnet for a rotor of the motor is mainly developed for an electric car because such a synchronous motor exhibits high efficiency.
Conventionally, synchronous motors of this type are widely used in a factory automation field in industry, and they are also suited for use in a field of electric cars while the basic control methods of the synchronous motors of this type are essentially the same both in the factory automation field and the electric vehicle field.
In a conventional control method of a synchronous motor for use in a factory automation field, when an overcurrent of a drive power device for driving a power motor is detected, electric current supply to the motor is instantaneously cut off to control the overcurrent of the power device so that the current supply to the motor is completely and immediately cut off.
However, in the case of an electric car which is driven using an electrically-powered motor, if the motor is suddenly controlled in the same manner as in the factory automation, there may cause a danger that the electric car may suddenly and unexpectedly stop and a behind car may collide, and further when a front car suddenly stops, it is impossible to avoid a front danger. On the other hand, when an overcurrent is detected, failure to interrupt the current supply may result in serious damage to the motor power device such as a fire occurrence of a motor drive unit and the like control circuit in the electric car.
In order to avoid such a problem involved in the conventional electrically-powered motor vehicles, in the disclosure of U.S. Pat. No. 5,592,355, there is suggested a motor control circuit which provides for improved ON/OFF switch safety in an electric car operation by temporarily interrupting a motor power supply as a means of eliminating an overcurrent supply to the motor when an overcurrent is detected, and in the case where a period integrating the overcurrent detection time exceeds a predetermined time limit, the motor power supply is completely shut out.
In this construction, even when an overcurrent is detected, the current supply is not completely stopped but merely temporarily interrupted, and the current supply for motor drive is retrieved when the current supply is appropriately reduced by eliminating the overcurrent. In this construction, however, when the ON/OFF switch of electric current supply to the motor is frequently repeated, a variation in torque of the motor is increased, which is offensive to a driver and passengers.
SUMMARY OF THE INVENTION
The present invention has been developed to solve these problems and has an essential object to provide an improvement of a current control apparatus with an overcurrent protective function protecting a motor and a drive control circuit with suppression of overcurrent in an electric vehicle in which an overcurrent to a motor is detected to be appropriately suppressed to thereby secure protection of the drive control circuit for the motor and enhance safety of the vehicle.
In order to achieve the object mentioned above, the present invention provides a current control apparatus with an overcurrent protective function for a motor which comprises: a current detecting unit for detecting a current value to be supplied to the motor for driving the motor; a current control section for determining the current value to be supplied to the motor based on a motor rotational command fed from an external portion and controlling the current value to be supplied to the motor by judging whether the current value detected by the current detecting unit is of an overcurrent level exceeding a prescribed value or a normal level which is not greater than the prescribed value. In this construction, when the current value detected by the current detecting unit is of an overcurrent level, the current control section restrains the current value to be supplied to the motor irrespective of the external motor rotational command, and when the current value detected by the current detecting unit is of the normal level, the current value to be supplied to the motor is restored to an original non-restraint level.
By the arrangements as described above, according to the present invention, when the current flowing through the drive power device of the electric car exceeds the prescribed value, the current supply is restrained in this manner, and when the current is controlled to be equal to or lower than the prescribed value, the current supply state is restored to the normal operation state. Thus, it is possible to prevent each of the parts of the car from being damaged, and secure safety of the car against danger such as collision due to sudden control to stop. Moreover, a danger can be avoided even when overcurrent is generated, having a large tolerance to a noise which may be caused when detecting the current, eliminating sudden variation in motor torque.
REFERENCES:
patent: 3803454 (1974-04-01), Higuchi
patent: 4090114 (1978-05-01), Thompson
patent: 4423362 (1983-12-01), Konrad et al.
patent: 4514665 (1985-04-01), Melocik et al.
patent: 5461531 (1995-10-01), Tuchiya et al.
patent: 5592355 (1997-01-01), Ikkai et al.
patent: 5757161 (1998-05-01), Ikkai et al.
Ikkai Yasufumi
Kishibe Taro
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Sherry Michael J.
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