CONTROL METHOD OF ELECTRIC VEHICLE

Abstract: A control method of an electric vehicle in which a frictional contact of rotating or stationary wheels of the electric vehicle to a rail road is recovered again when the wheels are in a slipping condition which is deter­ mined y a variable concerning rotation of the wheels exceeding a detection level which is determined by a sum of an instructed vehicle acceleration and a gradient accelerat­ ion detemined by an inclination of the rail road.

Description: The present invention relates to a control method of an electric vehicle for restricting a slippage of rotating or stationary wheels of the vehicle with respect to a rail road and, particularly, such method by which a reliability of detection of the slippage is improved. An example of known control methods is disclosed in "Electric Vehicle Science", Journal of Electric Vehicle Research Organization, 1987, March, page 30 (Fig. 15). The control method disclosed therein comprises a detection of rotation frequency of a rotary shaft of an induction motor controlled by a VVVF inverter, i.e., wheels of a vehicle, a generation of a slip signal or glide signal when a differentiation of the rotation frequency exceeds a constant detection level, a reduction of slip frequency which determines a frequency of the VVVF inverter and a restriction of the slippage. For example, when a driving force given by the induction motor to the wheels during power running control exceeds a maximum driving force (without slippage), the rotation frequency of the induction motor increases abruptly due to slippage. A VVVF inverter control device produces a slip signal when the differentiation of the rotation frequency exceeds a predetermined detection level upon which the slip frequency is reduced to reduce an output torque of the induction motor to thereby recover an optimum friction of the wheels to the rails. Similarly, for a slippage during braking control, the friction of the wheels to the rails is recovered again by reducing the slip frequency to restrict a braking force. It has been known, however, that the time differentiation of the rotation frequency depends upon rail road condition along which the vehicle runs. For example, when the vehicle runs along a down-hill rail road during power running control, the time differentiation increases. On the contrary, it is reduced when the vehicle runs along an up-hill rail road. Since the conventional control method of electric vhicle detects a slippage condition on the basis of a constant detection level, there is a case where a non-slip condition is detected as a slippage or an actual slipping condition can not be detected when the vehicle runs along an inclined rail road. An object of the present invention is to provide a control method of electric vhicle capable of detecting exactly and reliably an actual slippage. According to the present invention, a detection level is changed according to a sum of a vehicle acceleration and an acceleration due to inclination so that the detection level is corrected correspondingly to an actual acceleration of the vehicle to improve the reliability of detection of slippage. The single drawing shows an explanatry graph showing a variation of detection level according to an embodiment of the present invention. An embodiment of the present invention will be described with reference to the drawing. The drawing shows a time variation of a slip detection level obtained by the present invention, in which α₀ is a vehicle acceleration corresponding to an instruction value given to an induction motor, α₁ is a gradient acceleration corresponding to an inclination of a rail road and D is a slip detection level which varies according to a sum of the vehicle acceleration α₀ and the gradient acceleration α₁. For example, during power running control, the vehicle acceleration α₀ which is determined by a driving instruction of vehicle is constant. However, assuming that the rail road becomes down-hill at a time instance t₀ and a gradient thereof increases gradually, the gradient acceleration α₁ increases with time. The gradient acceleration may be preliminarily set as a rail road information or detected time to time by a suitable detector which is not shown. The slip detection level D, in this case, is a sum ( α₀ + α₁) of the vehicle acceleration α₀ and the gradient acceleration α₁ which increases in the same manner as that of the gradient acceleration α₁. Therefore, an erroneous detection of slippage is avoided since the detection level D increases even if the time differentiation of the rotation frequency of the induction motor. For a case of up-hill rail road, the detection level D decreases since the gradient acceleration α₁ becomes negative, and, therefore, a slippage can be detected reliably even if the time differentiation of the rotation frequency decreases. On the other hand, since, during a braking control in a down-hill running, the vehicle acceleration α₀ is negative, the gradient acceleration α₁ causes an absolute value of the detection level D to be decreased, making the slip detection reliable. During a braking control in an up-hill running, the gradient acceleration α₁ makes the detection level D higher, preventing an erroneous detection of slippage. In this manner, even when the gradient of the rail road changes at the time instance t₀ , the detection level D is corrected by the gradient acceleration α₁. Therefore, it becomes possible to detect reliably and rapidly an occurence of slippage of the wheels. Although, in the above mentioned embodiment, the slippage or gliding is detected according to the time differentiation of rotation frequency, i.e., an amount of acceleration, the same effect can be obtained by using a time differentiation of acceleration with a time differentiation of the vehicle acceleration α₀ and a time differentiation of the gradient acceleration α₁ being taken into consideration. A driving means for driving the vehicle is not limited to the induction motor. Other motors can be used. Further, the restriction of slippage or gliding may be performed by other method than the reducton of slip frequency. As mentioned, according to the present invention, the detection level of slippage is changed on the basis of the sum of the vehicle acceleration and the gradient acceleration so that it is corrected correspondingly to an actual acceleration of the vehicle. Therefore, the reliability of slip detection for the electric vehicle is improved.

Claims: A control method of an electric vehicle in which a frictional contact of rotating or stationary wheels of said electric vehicle to a rail road is recovered again when said wheels are in a slipping condition which is determined by a variable concerning rotation of said wheels exceeding a detection level, comprising the step of changing said detection level according to a sum of an instructed vehicle acceleration (α₀) and a gradient acceleration (α₁) determined by an inclination of said rail road. The control method as claimed in claim 1, wherein said gradient acceleration (α₁) is given preliminarily as a rail road information. The control method as claimed in claim 1, wherein said gradient acceleration (α₁) is detected from time to time by a suitable means. The control method as claimed in any of claims 1 to 3, wherein said variable is a time differentiation of rotation frequency of said wheels.

Inventors: NAKAMOTO, NORIAKI C/O MITSUBISHI DENKI K. K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: B60L3
IPC codes: B60L3, B60L15