Method and device for limiting electrical current supplied to the motor of an electric vehicle

• US 5,341,077 A
• Filed: 02/03/1993
• Issued: 08/23/1994
• Est. Priority Date: 02/03/1993
• Status: Expired due to Term

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Chen, Tshaw-Chuang, Shieh, Yaw-Shih, Chang, Hong-Shi, Yang, Huan-Jen
• Primary Examiner(s): Wysocki, Jonathan
• Application Number:
  US08/012,889
• Time in Patent Office: 566 Days
• Field of Search: 318/432, 318/434, 318/471, 318/362, 318/366, 361/23, 361/24, 361/25-27, 361/31, 361/103, 388/811, 388/817, 388/903, 388/934
• US Class Current: 318/434
• CPC Class Codes: H02H 7/0833 for electric motors with control arrangements
• CPC Class Codes: H02H 7/0852 directly responsive to abnormal temperature by using a temperature sensor in a control circuit H02H7/0833
• CPC Class Codes: H02H 7/0858 by reversing, cycling or reducing the power supply to the motor

Abstract

A current limiting device to limit the maximum allowable electric current to be supplied to a motor in driving an electric vehicle. The current limiting device includes (a) a first thermal switch to prevent the power switching element of the motor from being abnormally overheated, (b) a second thermal switch to prevent the motor from being abnormally overheated, and (c) a brake switch. The three switches altogether and in association with a certain hysteresis band work to switch the limits of the electric current passing through the motor between two or more predetermined electric current values. Under normal operating conditions, the limit of the current is set at a high level which is associated with a hysteresis action, and when one of the thermal switches or the brake switch is actuated, the limit of the electric current is switched to a lower value which is still associated with a hysteresis action.

Claims

1. A method for limiting electrical current passing through an electric motor which is used in driving an electrical vehicle, said method comprising the steps of:

obtaining a current limiting apparatus, said current limiting apparatus containing a gate driver which contains a first thermal switch connected to a power switching element, a second thermal switch connected to said motor, and a brake switch,

setting a high and at least a first and a second lower allowable current limits for said current limiting apparatus, said first lower current limit being higher than second lower current limit but lower than said high current limit, whereby said current limit initially will be set at said high level, each of said current limits is set according to a hysteresis operation of said electric motor;

shifting said current limit to said first lower level when either said first thernal switch or said second thermal switch is actuated due to overheating, or when said braking switch is actuated when a brake is applied;

further shifting said current limit to said second lower level when said overheating presists; and

shifting said current limit from a lower level to a higher level as soon as said power switching element, said motor and said brake switch are in an normal state.

2. The method for limiting electrical current passing through an electric motor according to claim 1 wherein said current limiting apparatus comprising:

a low pass amplifier for amplifying a first electrical signal corresponding to the current supplied to said electric motor from a power source and removing noise from said first electrical signal and producing a second electrical signal;

a plurality of thermal switches operable at various temperature levels to produce a thermal signal;

a brake switch operable in association with a brake device of said vehicle to produce a braking signal;

a gain switching amplifier for receiving said second electrical signal, said thermal signal and said braking signal to determine a gain and produce a current limiting signal representing a current limit;

a hysteresis level detector for detecting the level of a hysteresis of said electric motor at each level of the current supplied to said electric motor, and producing a range signal to define a range of said current limit; and

a pulse width modulator for controlling the level of current supplied to said electric motor according to said current limiting signal and said range signal.

3. The method for limiting electrical current passing through an electric motor according to claim 1 wherein said first lower level is no greater than 50% of of said high level.

4. The method for limiting electrical current passing through an electric motor according to claim 1 wherein said first thermal switch, said second thermal switch, and said brake switch are connected in series.

5. A current limiting apparatus for limiting electrical current passing through an electric motor comprising:

a low pass amplifier for amplifying a first electrical signal corresponding to the current supplied to said electric motor from a power source and removing noise from said first electrical signal and producing a second electrical signal;

a plurality of thermal switches operable at various temperature levels to produce a thermal signal;

a brake switch operable in association with a brake device of said vehicle to produce a braking signal;

a gain switching amplifier for receiving said second electrical signal;

said thermal signal and said braking signal to determine a gain and produce a current limiting signal representing a current limit;

a hysteresis level detector for detecting the level of a hysteresis of said electric motor at each level of the current supplied to said electric motor, and producing a range signal to define a range of said current limit; and

a pulse width modulator for controlling the level of current supplied to said electric motor according to said current limiting signal and said range signal.