JPH07257417A - Electric motor drive control device for electric steering device - Google Patents

Abstract

PURPOSE:To improve reliability and stability of an electric steering device by providing with a processing device for outputting a direction signal and a torque signal according to a steering amount and a direction determining circuit having a dead zone taking a designated reference value as a center and corresponding to a steering torque and driving it only by the processing device within the dead zone. CONSTITUTION:A direction determining circuit is provided with two comparators 52, 53 and respective output terminals are connected with a plus and minus terminals of a differential amplifier 35 and reference voltage Vref1 and Vref2 are supplied. These reference voltages are determined in a relation that Vref1> Vref>Vref2 to the reference voltage Vref in a state that generates no steering torque and a low level signal is outputted from the comparators 52, 53 to drive FET 38-41 ON if the output of the differential amplifier 35 is between the reference voltage Vref1, 2. A direction determining circuit 51 having a dead zone adjacent to the reference voltage Vref and brake control can be performed even if the steering torque is not generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to drive an electric motor by PWM control in response to steering of a steering wheel.
The present invention relates to an electric motor drive control device of an electric steering device that applies a steering force to steering wheels.

[0002]

2. Description of the Related Art By generating an auxiliary steering torque in a motor by PWM control based on detected values such as steering torque and steering rotation speed applied to a steering wheel,
An electric steering system designed to reduce steering force
For example, JP-A-61-271168 and JP-A-61-2750.
No. 57, etc.

Conventionally, an electric motor drive circuit for driving and controlling the electric motor has an H-shaped bridge circuit composed of four bipolar transistors or field effect transistors whose base is connected to an output port of the CPU, and is output from the CPU. The control signal drives a pair of transistors on opposite sides of the bridge circuit, whereby the electric motor is PWM-controlled.

However, if the CPU or its output section malfunctions or an output abnormality due to electromagnetic interference, a malfunction, software runaway, or the like occurs due to some circumstances, proper control of the electric motor becomes difficult. It is difficult to detect all such failures by using a method such as WDT (watch dog timer) or current detection. A control method in which two separately provided PWM control signals are synchronized and the electric motor is driven only when their outputs match each other can be considered, but since the electric motor is driven by a duty ratio control equivalent to 20 kHz. , Practically difficult. For these reasons, it has been an important problem to ensure sufficient reliability in the drive control of the electric motor in the conventional electric steering system that drives the electric motor by PWM control.

As a motor drive control device for coping with such a problem, there is a circuit configuration shown in FIG. The electric motor drive control device 10 includes a control circuit 31 connected to the steering angle sensor 9 (20) and the steering torque sensor 30, and a drive circuit 32 connected to the electric motor 12.

The control circuit 31 determines a driving direction and a driving torque of the electric motor 12 based on the output of the steering angle sensor 9 (20) and outputs the CPU 33 as an arithmetic unit.
A direction discriminating circuit 34 for determining and outputting the driving direction of the electric motor 12 based on the output of the steering torque sensor 30.

The steering torque sensor 30 is composed of a known operating transformer or the like mounted on a steering rod that is driven by the electric motor 12 to steer the front wheels, and is connected to the CPU 33 via a differential amplifier 35. The secondary coil is connected to the negative terminal of the operational amplifier 36 forming the differential amplifier 35, and the other secondary coil is connected to the positive terminal.

The CPU 33 outputs an output terminal OUT1 for outputting an ON / OFF signal for ON-driving the four FETs 38 to 41 constituting the switch circuit 37 of the drive circuit 32 described later.
To OUT4 are connected to the input terminals of the NAND gates 42 to 45, respectively, and P for PWM controlling the electric motor 12 is provided.
Output terminals OUT5 and OUT6 that output WM signals are N
AND gates 42 and 43 and NAND gates 44 and 45
It is connected to the. Of course, depending on the circuit configuration, the NAND gate can be replaced with an AND gate, and a plurality of logic gates can be used to obtain a logical product.

The direction discriminating circuit 34 includes a comparator 46 in which the output terminal of the differential amplifier 35 is connected to the plus terminal and the reference voltage Vref is connected to the minus terminal.
The output of the comparator 46 is two output lines 47.4.
8, the output line 47 on one side is connected to the NAND gate 43 and the NAND gate 45 via the NOT gate 49, and the output line 48 on the other side is the NAND gates 42 and N.
It is connected to the AND gate 44.

The drive circuit 32 is the switch circuit 3 described above.
In addition to 7, a gate drive circuit 50 is provided. The switch circuit 37 includes four field effect transistors (FE
T) 38-41 H-shaped bridge circuit. The gates of the FETs 38 to 41 are connected to the NANDs 42 to 45 via the gate drive circuit 50. FET3 corresponding to the input terminal of this switch circuit 37
The drain of 8.39 is connected to a battery (not shown) through a relay, and the sources are FETs 40 and 4, respectively.
1 connected to the drain. And FET40 ・ 4
1 has a source grounded. A connection portion between the source of the FET 38 and the drain of the FET 41, which corresponds to the output terminal of the switch circuit 37, and the source of the FET 39 and the FET 40.
The electric motor 12 is connected between the connection part with the drain of.

The direction signal and P output from the CPU 33
When the WM signal and the direction signal output from the direction determination circuit 34 match, the direction signal and PW output from the corresponding NAND gates 42 to 45 to the gate drive circuit 50.
A corresponding FET of the switch circuit 37 based on the M signal
38 to 41 are driven. Therefore, the electric motor 12 is driven in the predetermined direction by the PWM control.

However, when the output from the CPU 33 does not match the output from the direction discriminating circuit 34, the direction signals and the PWM signal are not output from the NAND gates 42 to 45, so that the FETs 38 to 41 of the switch circuit 37 are driven. No, and therefore the electric motor 12 is not driven. In this way, due to some reason, the CPU 33 has a failure or an output abnormality,
Reliability can be secured against malfunctions due to electromagnetic interference or software runaway.

[0013]

According to the above construction, the low or high level signal is output from the comparator 46 based on the comparison between the voltage corresponding to the steering torque output from the differential amplifier 35 and the predetermined reference voltage Vref. It is output and the driving direction of the electric motor 12 is determined. However, in the vicinity of the reference voltage Vref where the steering torque is not actually generated, there is a lot of noise, and the reference voltage Vref easily varies, so that the determination of the steering direction tends to be unstable.

The present invention has been devised in order to eliminate such disadvantages of the prior art, and its main purpose is to:
In an electric steering system that steers the steered wheels by driving the electric motor by PWM control according to the steering of the steering wheel, the reliability is sufficiently improved, and steering torque is not generated. An object of the present invention is to provide an improved motor drive control device that can stabilize the control.

[0015]

According to the present invention, such a purpose is to provide a control circuit for determining a driving direction and a driving torque of an electric motor according to steering of a steering wheel, and a bridge consisting of four transistors. A power source is connected to an input terminal of the circuit and the electric motor is connected to an output terminal, and a drive signal is supplied to a pair of transistors on opposite sides of the bridge circuit based on an output of the control circuit to drive the electric motor. A motor drive control device for an electric steering system, comprising a drive circuit for drive control, wherein the control circuit comprises:
The direction determining circuit includes a computing unit that outputs a direction signal and a torque signal according to the steering amount of the steering wheel, and a direction determining circuit that outputs a direction signal according to the steering torque of the steering wheel. A dead zone centered on a predetermined reference value is provided, and outside the dead zone, when the direction signal output from the arithmetic unit and the direction signal output from the direction determination circuit match, the one set An electric motor drive control device for an electric steering system, characterized in that the drive circuit is driven so as to supply a drive signal to the transistor of, and the drive circuit is driven only by the arithmetic unit within the dead zone. Achieved by providing.

[0016]

According to this structure, the driving direction and timing of the electric motor output from the arithmetic unit can be confirmed by the output from the direction discriminating circuit, and the electric motor is driven only when the bidirectional signals match. If they do not match, the electric motor is not driven, and the reliability is improved. Further, by providing a dead zone in the direction determination circuit, it is possible to cope with the timing deviation from the signal from the arithmetic unit and the variation due to noise, and at the same time, the brake control can be added to the electric motor when the steering torque is not generated. it can.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to specific embodiments shown in the accompanying drawings.

FIG. 1 is a schematic configuration diagram of a front and rear wheel steering device to which the present invention is applied. In FIG. 1, the steering wheel 1 is fixed to the upper end of the steering shaft 2,
Further, it is connected to the front wheel steering gear mechanism 3 composed of a rack and pinion mechanism via the steering shaft 2. The front wheel steering gear mechanism 3 is composed of a pinion gear 4 that rotates integrally with the steering shaft 2 and a rack 5 that meshes with the pinion gear 4. The front and rear steering gear mechanisms 3 are provided on both ends of the rack 5 via tie rods 6L and 6R and knuckle arms 7L and 7R, respectively. Front wheels 8L and 8R are connected.

A steering angle sensor 9 including, for example, a rotary encoder for detecting the rotation angle of the steering shaft 2 is attached to the steering shaft 2. The steering angle sensor 9 is connected to a control device 10 including a CPU and the like, and outputs a signal indicating the steering angle of the steering wheel 1 to the control device 10. If the steering angle detected by the steering angle sensor 9 is differentiated,
The steering speed of the steering wheel 1 can be detected. Vehicle speed sensors 11L and 11R connected to the control device 10 are attached to the front wheels 8L and 8R, respectively, and a signal representing the vehicle speed is output to the control device 10.

An electric motor 12 driven and controlled by the control device 10 is arranged on the rear wheel side. This electric motor 12
Is connected to a rear wheel steering gear mechanism 14 which is a rack and pinion mechanism via a bevel gear mechanism 13. The rear wheel steering gear mechanism 14 is provided for the electric motor 1.
It is provided with a pinion gear 15 that rotates integrally with the output shaft of 2 and a rack 16 that meshes with the pinion gear 15. At both ends of the rack 16, left and right rear wheels 19L and 19L via tie rods 17L and 17R and knuckle arms 18L and 18R, respectively. 19R is connected.

A rear wheel steering angle sensor 20 including a differential transformer is attached to the rack 16 in order to detect the moving distance in the axial direction. This rear wheel steering angle sensor 20
Is connected to the control device 10, and the rear wheel steering angle sensor 2
Rear wheels 19L and 19R detected based on 0 differential signal
A signal representing the steering angle of the control unit 10 is output to the control device 10. Vehicle speed sensors 21L and 21R are attached to the rear wheels 19L and 19R, respectively, and are connected to the control device 10.

FIG. 2 is a schematic circuit configuration diagram of the control device 10 according to the present invention. Since the main part of the control circuit 31 and the drive circuit 32 are substantially the same as the configuration shown in FIG. 3, common parts are denoted by the same reference numerals as in FIG. 3, and only different parts will be described below.

In the present embodiment, the direction discriminating circuit 51 is
It is provided with two comparators 52 and 53. Among these, one of the comparators 52 is configured such that the output terminal of the differential amplifier 35 is connected to the positive terminal and the first reference voltage Vref1 is supplied to the negative terminal. In the other comparator 53, the output terminal of the differential amplifier 35 is connected to the minus terminal, and the second reference voltage Vref2 is supplied to the plus terminal. The output terminal of one comparator 52 is connected to the NAND gates 42 and 44, and the output terminal of the other comparator 53 is connected to the NAND gates 43 and 45.

On the other hand, the first and second reference voltages Vref1 and Vref2
Is the reference voltage Vre when the steering torque is not generated.
It is set to have a relationship of Vref1>Vref> Vref2 with respect to f. One comparator 52 outputs a high level signal when the output of the differential amplifier 35 is equal to or higher than the first reference voltage Vref1, and outputs a low level signal when the output is equal to or lower than Vref1. In the other comparator 53, the output of the differential amplifier 35 is the second reference voltage V
When it is less than ref2, a high level signal is output, and when it is more than Vref2, a low level signal is output.
If the output of the differential amplifier 35 is between the first reference voltage Vref1 and the second reference voltage Vref2, both comparators 5
A low level signal is output from 2.53 and the switch circuit 3
All the FETs 38 to 41 of No. 7 are turned on. As described above, by configuring the direction determining circuit 51 so as to have the dead zone near the predetermined reference voltage Vref, it is possible to cope with the timing deviation with the CPU 33, the variation due to noise, etc., and at the same time, the steering torque is generated. Brake control can be performed as electric motor control in the non-operating state.

[0025]

As described above, according to the present invention, in the electric steering system that drives the electric motor by PWM control to steer the steered wheels, the driving direction of the electric motor is changed according to the operation amount of the steering wheel. In addition to the CPU that determines the drive torque, a direction determination circuit that determines only the drive direction of the electric motor is provided, and the FET of the switch circuit is driven only when the direction signals output from both sides match. By doing so, the reliability in drive control of the electric motor can be significantly improved. In addition, by providing a dead zone in the direction determination circuit, it is possible to cope with timing deviation from the signal from the arithmetic unit and variations due to noise, and at the same time, perform brake control as electric motor control when steering torque is not generated. You can

[Brief description of drawings]

FIG. 1 is a schematic overall configuration diagram of a front and rear wheel steering device to which the present invention is applied.

FIG. 2 is a schematic circuit configuration diagram of an electric motor drive control device according to the present invention.

FIG. 3 is a schematic circuit configuration diagram of a conventional electric motor drive control device.

[Explanation of symbols]

1 ... Steering wheel, 2 ... Steering shaft, 3 ... Front wheel steering gear mechanism, 4 ... Pinion gear, 5 ... Rack, 6L / 6R ... Tie rod, 7L / 7R
... Knuckle arm, 8L / 8R ... Front wheel, 9/20 ... Steering angle sensor, 10 ... Control device, 11L / 11R ... Vehicle speed sensor, 12 ... Electric motor, 13 ... Bevel gear mechanism, 14 ... Rear wheel steering gear mechanism, 15 ... Pinion gear, 16 ... Rack, 17L / 17R ... Tie rod, 18L / 18R ... Knuckle arm, 19L / 190 ... Rear wheel, 21L / 21R
... vehicle speed sensor, 30 ... steering torque sensor, 31 ... control circuit, 32 ... drive circuit, 33 ... CPU, 34 ... direction discriminating circuit, 35 ... differential amplifier, 36 ... operational amplifier, 37 ... switch circuit, 38-41 ... FET , 42-45 ... NAND
Gate, 46 ... Comparator, 47/48 ... Output line, 4
9 ... NOT gate, 50 ... Gate drive circuit, 51 ...
Direction discriminating circuit, 52/53 ... Comparator

Claims (1)

[Claims] 1. A control circuit for determining a driving direction and a driving torque of an electric motor according to steering of a steering wheel, a power source is connected to an input terminal of a bridge circuit composed of four transistors, and the electric motor is connected to an output terminal. A motor drive control of an electric steering device, which is connected to the bridge circuit and supplies a drive signal to a pair of transistors on opposite sides of the bridge circuit based on an output of the control circuit to drive and control the motor. In the device, the control circuit outputs a direction signal and a torque signal according to the steering amount of the steering wheel, and a direction determination circuit that outputs a direction signal according to the steering torque of the steering wheel. The direction discriminating circuit has a dead zone centered on a predetermined reference value. Outside the dead zone, the direction discriminating circuit outputs from the arithmetic unit. The drive circuit so as to supply a drive signal to the one set of transistors when the direction signal output from the direction determination circuit and the direction signal output from the direction determination circuit coincide with each other, and the arithmetic unit in the dead zone. An electric motor drive control device for an electric steering device, characterized in that the drive circuit is driven only by itself.