JPH0569833A - Electrically-operated power steering device - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To eliminate radio noise generated from the motor drive circuit of the electric power steering system. [Configuration] Four switching elements FET2a,
2b, 2c, 2d and a motor drive circuit 9 composed of a bootstrap circuit, and based on the detected torque from the torque sensor 6 and the vehicle speed detected from the vehicle speed sensor 11, etc., the motor 1 is switched on and off and the polarity is switched to obtain the steering force assisting amount. And a control device 5 for controlling the. ON / OFF of the FETs 2a, 2b, 2c, 2d forming the bridge circuit is controlled by a signal from the controller 5. And the connection point between the FETs 2a and 2c and the FETs 2b and 2d
Both terminals of the motor 1 are connected to the connection point with. Radio noise does not occur because the booster circuit required in the conventional configuration is not used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional electric power steering system. This device includes a motor 1 for assisting steering force and four field effect transistors (hereinafter referred to as FE).
(Referred to as “T”) 2a, 2b, 2c, 2d, a motor drive circuit 17 composed of a bridge circuit, a booster circuit 14 for obtaining a drive voltage for the two FETs 2a, 2b of the motor drive circuit 17, a motor drive circuit 17 A key switch 12 and a fail relay 3 provided between the vehicle and a main power source (battery) 4, a torque sensor 6 for detecting an input torque of a steering shaft, a vehicle speed sensor 11 for detecting a vehicle speed, and a torque. The control device 15 controls the motor 1 and the fail relay 3 based on the torque detected by the sensor 6 and the torque detected by the vehicle speed sensor 11. In addition, 7 is an amplifier and 8 is a resistor. Again 1
6 is a motor control circuit.

[0003]

However, the above-mentioned conventional configuration has a problem that it is necessary to take measures against the radio noise constantly generated from the booster circuit 14.

[0004]

In order to solve the above problems, the present invention detects a motor connected to a steering shaft through a connecting means for assisting a steering force, and an input torque of the steering shaft. Torque sensor, and a motor control means for controlling the steering force assisting amount by switching the motor on and off and switching the polarity based on the torque detected by the torque sensor, and on / off by a signal from the motor control means. First controlled
A motor drive including four switching elements, second, third and fourth switching elements, and first and second bootstrap circuits for obtaining driving voltages for these switching elements, and a bridge circuit configured by the switching elements. A circuit, and the motor is provided at a connection point between the first switching element and the third switching element and a connection point between the second switching element and the fourth switching element of the motor drive circuit. It is connected.

[0005]

According to the present invention, since the bootstrap circuit is used to obtain the driving voltage of the switching element, radio noise is not always generated.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electric power steering system according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention and shows a schematic configuration of the entire electric power steering apparatus. In FIG. 1, the same parts as those in FIG. 4 are designated by the same reference numerals. This device includes a motor 1 coupled to a steering shaft via coupling means (not shown) for assisting the steering force, and FETs 2a, 2b, 2c, 2d which are four switching elements.
And a key switch 1 provided between a motor drive circuit 9 including a bootstrap circuit and a main power supply (battery) 4.
2 and the relay 3, the torque sensor 6 for detecting the input torque of the steering shaft, the vehicle speed sensor 11 for detecting the vehicle speed, the detected torque from the torque sensor 6 and the detected vehicle speed from the vehicle speed sensor 11, etc. The control device 5 controls the steering force assist amount by switching the motor 1 on and off and switching the polarity. By the signal from the control device 5, the FETs 2a, 2b, 2
ON / OFF of c and 2d is controlled. Further, the FETs 2a, 2b, 2c and 2d that form the motor drive circuit 9 form a bridge circuit, and both ends of the motor 1 are connected to the connection point between the FETs 2a and 2c and the connection point between the FETs 2b and 2d. The child is connected. The whole of these is referred to as a motor control circuit 10.

When the motor 1 of this apparatus is normally rotated, as shown in FIG. 2 (a), the FET 2d is turned on by the controller 5 and then the FET 2a is outputted by the PWM signal outputted to the point E of the controller 5. Is turned on to obtain the required motor drive current. In this case, the current flows in the direction of I _a .

When the motor 1 is rotated in the reverse direction, as shown in FIG.
As shown in (b), the control device 5 turns on the FET 2c, and then the PWM signal output to the point F of the control device 5 turns on the FET 2b to obtain the required motor drive current.
In this case, the current flows in the direction of _Ib .

As described above, according to this embodiment, the bootstrap circuit is used to obtain the drive voltage of the FETs 2a and 2b. When the motor is not driven, no radio noise is generated and the conventional configuration is required. It is no longer necessary to take measures against radio noise for the booster circuit. Further, the bootstrap circuit can configure the motor drive circuit at a lower cost than the booster circuit.

[0010]

As described above, according to the present invention, since the bootstrap circuit is used to obtain the driving voltage of the switching element, radio noise is not always generated.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an electric power steering device according to an embodiment of the present invention.

2A and 2B are waveform charts showing the operation of the switching element of the same device.

FIG. 3 is a circuit diagram of a motor drive circuit of the device.

FIG. 4 is a circuit diagram of a conventional electric power steering device.

[Explanation of symbols]

 1 Motor 2a, 2b, 2c, 2d FET 3 Relay 5 Control device 6 Torque sensor 9 Motor drive circuit 10 Motor control circuit 11 Vehicle speed sensor 12 Key switch 13a, 13b Bootstrap circuit

Claims (1)

[Claims] 1. A motor coupled to a steering shaft via coupling means for assisting a steering force, a torque sensor for detecting an input torque of the steering shaft, and the motor based on the torque detected by the torque sensor. Motor control means for controlling the steering force assisting amount by switching on and off and switching the polarities, and ON, OFF controlled by a signal from the motor control means.
And a motor drive circuit including four fourth switching elements and first and second bootstrap circuits for obtaining driving voltages for these switching elements, and a bridge circuit including the switching elements. An electric power connecting the motor to a connection point between the first switching element and the third switching element and a connection point between the second switching element and the fourth switching element of the motor drive circuit Steering device.