JPH02158455A - Overcurrent protecting method for motor-operated power steering - Google Patents

Abstract

PURPOSE:To prevent rupture of each switching element and runaway of a steering system by a method wherein chopper control is made on a number of main switching elements, formed in a bridge state in order to control the current of a motor, by means of a plurality of cut-off currents being different between two stages of upper and lower stages. CONSTITUTION:A current detector 2 is connected to a battery 1, and a number of main switching elements (FET) 3a - 3d arranged in a bridge state in order to control the direction of an amount of a current to a motor 5 are connected thereto. First and second cut-off current set circuits 6a and 6b to individually control the FET 3a - 3d at the upper and lower stages are disposed to a control circuit 6 to control the FET 3a - 3d. Namely, chopper control is made on the FET 3a - 3d by means of a plurality of cut-off currents different between the upper and lower stages. This constitution maintains a motor current at a value within the rated value of the FET even during rapid turn of a handle, resulting in prevention of rupture of the FET and runaway of a steering system.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an electric power steering device that reduces the steering torque of a steering system by electric power, and in particular to overcurrent protection of a main switching element (hereinafter referred to as FET). It is about the method.

(Prior art) In conventional devices of this type, the upper stage only switches the direction of rotation;
Always keep the fullie ON or OFF, and set the lower FET
Chopper control was performed at a constant current limit value.

(Problem to be solved by the invention) In the conventional device, when the handle is suddenly reversed,
Due to the influence of the motor's back electromotive force, etc., the rise ratio of the motor current changes, and as shown in Figure 3, a current that far exceeds the current limit value IM flows through the circuit, and this current flows through the FET. There was a problem that the rated value was exceeded and the FET was destroyed.

(Means for Solving the Problems) The overcurrent protection method for an electric power steering device of the present invention (hereinafter referred to as the present invention) provides a bridge for controlling the direction and amount of current supplied to the motor of an electric power steering device. By chopper controlling the configured FETs with two different current limit values for the upper and lower stages, the motor current is prevented from exceeding the FET's rated value even when the handle is suddenly reversed. , which attempts to solve the above-mentioned problems.

(Embodiment) An embodiment of the present invention will be described based on the drawings. In FIG. 1, l is a battery, 2 is a current detector, 3a, 3b,
3c and 3d are FETs arranged in a bridge shape to control the direction and amount of motor current, 4a, 4b, 4c, 4d
is an internal reverse diode in the FET, 5 is a motor, 6 is a control circuit that controls the above-mentioned FF and T, and the lower stage FF and T are controlled by the 1i current value setting circuit 6a which sets a current limit value called IMO, The circuit configuration is such that the lower FET is controlled by a second current limit value setting circuit 6b that has a current limit value called ITO.

When only the lower FET is turned off, the motor current performs flywheel and gradually decreases.

In other words, if the rate of rise of the motor current during the delay time A becomes larger than the rate of decrease of the motor current due to the flywheel, the current will increase indefinitely. Methods for preventing this include (1) shortening the delay time A, and (2) increasing the rate of decrease. The present invention attempts to increase the rate of decrease in the latter (2).

In other words, in addition to the current limit value command IMO, another current limit value command ITO that matches the rating of the element is set (however, ITO>I
Let it be MO. ) When the current feed bank value exceeds the set value, the upper FET (here 3a) is set to 0FFL.
, the motor current is regenerated to the battery as shown in FIG. By regenerating to the battery, the motor current rapidly decreases and can be kept within the second current limit value ITO as shown in FIG.

(Effects) As described above, the present invention utilizes a method of chopper-controlling the bridge-configured FET with two different current limit values for the upper and lower stages, so that even when the handle is suddenly reversed, Since the motor current can be kept within the rated value of the FET, there is an advantage in that it is possible to prevent destruction of the FET and, in turn, prevent the steering system from running out of control.

[Brief explanation of the drawing]

FIG. 1 shows a circuit diagram according to the present invention, FIGS. 2 and 3 are explanatory diagrams of regeneration states, and FIGS. 3 and 4 show commands and current waveforms. 1---------Battery 2---Current detector 3a + 3b + 3c + 3d---F
ET4a+4b+4c, 4d...--F E T
Internal reverse diode 5 ----------Motor 6 -------・In control circuit

Claims (1)

[Claims] In order to control the direction and amount of current supplied to the motor of the electric power steering device, the main switching element in a bridge configuration is chopper-controlled with two different current limit values for each of the upper and lower stages. Overcurrent protection method for electric power steering equipment.