JP2698913B2 - Control device for electric power steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device such as an automobile.

2. Description of the Related Art For example, there is known a power steering device for an automobile that includes a control device for controlling a current of an electric motor for applying an auxiliary steering force to a steering system based on an input torque of a steering shaft and a vehicle speed. Have been.

Such a power steering apparatus is based on a non-assisted steering state in which the electric motor does not assist the steering force when the ignition switch is turned on / off, high-speed running, an abnormality, and the like, and an input torque and a vehicle speed of the steering shaft. The state is switched to a normal auxiliary steering state in which the determined current target value is output as a current instruction value as it is. In order to set the power steering device in the non-assisted steering state, a clutch is provided between the motor and the steering system, a method of disconnecting the clutch to disconnect the motor from the steering system, and setting the current value of the motor to 0 without providing the clutch. There are ways to do that. However, in each case,
Simply disengaging the clutch or setting the current value of the motor to 0 results in an abrupt change in the auxiliary steering force, which not only gives the driver discomfort but also may cause danger.

Therefore, when switching from the normal auxiliary steering state to the non-auxiliary steering state, the applicant gradually changes the coefficient from 1 to 0, and outputs a value obtained by multiplying the target value of the current by this coefficient as a current instruction value. When switching from the non-assisted steering state to the normal assisted steering state, the coefficient is gradually changed from 0 to 1, and a value obtained by multiplying the current target value by this coefficient is output as a current instruction value. A new type of power steering system was proposed (see Japanese Patent Application Nos. 62-316740 and 62-316741).

Although the control device of the power steering device includes a microcomputer, as described above, the auxiliary steering when switching from the normal auxiliary steering state (or the non-auxiliary steering state) to the non-auxiliary steering state (or the normal auxiliary steering state) is performed. In the force adjustment state (state in which the indicated value of the output current is gradually increased or decreased regardless of the current target value),
Since the multiplication of the current target value and the coefficient is performed, the microcomputer needs a multiplication function. Some microcomputers do not have a multiplication function. In this case, a multiplication routine must be provided in the program. Further, since the multiplication time is long, the time until the output of the instruction value to the motor is correspondingly long, and it is necessary to lengthen the sampling period in consideration of this. For this reason, the phase delay with respect to the input output increases, and the steering system easily oscillates.

An object of the present invention is to provide a control device for an electric power steering device that solves the above-mentioned problem.

Means for Solving the Problems An apparatus according to a first aspect of the present invention determines a target value of a current of an electric motor for applying an auxiliary steering force to a steering system based on at least an input torque of a steering shaft. Non-auxiliary steering state where not performed, normal auxiliary steering state where current target value is output as current instruction value as it is, and auxiliary steering force adjustment state where current instruction value to be output is gradually increased or decreased regardless of current target value A control device for an electric power steering device that is switched to an upper limit value of a current instruction value in an auxiliary steering force adjustment state, and gradually decreases the upper limit value when a vehicle speed becomes higher than a predetermined value. When the vehicle speed becomes lower than the predetermined value, the upper limit value is gradually increased, and when the current target value is equal to or less than the upper limit value, the target value is increased. Output as 示値, when the target value of the current exceeds the upper limit value is characterized in that it is designed to output the upper limit value as an instruction value.

An apparatus according to a second aspect of the present invention determines a target value of a current of an electric motor for applying an auxiliary steering force to a steering system based on outputs of a torque sensor for detecting an input torque of a steering shaft and a vehicle speed sensor for detecting a vehicle speed, A non-auxiliary steering state in which the electric motor does not perform auxiliary steering, a normal auxiliary steering state in which the current target value is output as the current instruction value as it is, and an auxiliary in which the current instruction value to be output is gradually reduced regardless of the current target value. A control device for an electric power steering device that can be switched to a steering force adjustment state, wherein in an auxiliary steering force adjustment state, an upper limit value of a current instruction value is determined, and when an abnormality occurs in the sensor, the upper limit value is set. When the current target value is less than or equal to the upper limit value, the target value is output as the indicated value, and the current target value exceeds the upper limit value. The case is characterized in that it is designed to output the upper limit value as an instruction value.

In the first aspect of the invention, in the assist steering force adjustment state, when the vehicle speed exceeds a predetermined value, the command value of the current output from the control device does not exceed the upper limit value that gradually decreases, and the vehicle speed does not exceed the upper limit value. Is smaller than the predetermined value, the command value of the current output from the control device does not exceed the upper limit value that gradually increases. Therefore, the auxiliary steering force gradually decreases or increases, and does not rapidly change.

In the case of the second invention, in the auxiliary steering force adjustment state, when an abnormality occurs in the sensor, the instruction value of the current output from the control device does not exceed the upper limit value that gradually decreases, and therefore, the auxiliary steering force is adjusted. The force gradually decreases and does not change rapidly.

Further, in any of the first and second inventions, it is only necessary to gradually change the upper limit value of the current and compare it with the target value, so that there is no need for multiplication. Therefore, there is no need to lengthen the time until the output of the current instruction value to the motor and the sampling period, and it is possible to suppress the oscillation of the steering system. Since the microcomputer does not require a multiplication function, an inexpensive and high-performance electric power steering apparatus can be obtained without using a high-performance microcomputer.

Embodiment FIG. 1 shows a schematic configuration of an electric power steering apparatus for an automobile.

This device includes an electric motor with a speed reducer (10) for assisting a steering force, a clutch (11) provided between the motor (10) and a steering system, and a device for detecting an input torque of a steering shaft. Control for controlling the motor (10) and the clutch (11) based on the output of the torque sensor (12), the vehicle speed sensor (13) for detecting the vehicle speed, and the torque sensor (12) and the vehicle speed sensor (13). Equipment (1
4) and

Although not shown, the motor (10) is connected to an appropriate portion of the steering system, for example, an output shaft of a steering shaft or a steering gear via a clutch (11). The torque sensor (12) is, for example, a potentiometer that detects the torsion of a torsion bar provided between the input shaft and the output shaft of the steering shaft. The control device (14) includes a motor drive circuit (15), a clutch drive circuit (16), and a microcomputer (17) for controlling these. Since the torque sensor (12), the vehicle speed sensor (13), the motor drive circuit (15), and the clutch drive circuit (16) can have any known configurations, detailed description will be omitted.

The control device (14) constantly monitors the outputs of the torque sensor (12), the vehicle speed sensor (13), the motor drive circuit (15), the clutch drive circuit (16), and the like to determine the state of the vehicle. I do. Further, a target value (hereinafter, simply referred to as a target value) of the current of the motor (10) is determined based on the input torque of the steering shaft and the vehicle speed. Then, according to the state of the vehicle, the power steering device is in a non-auxiliary steering state in which auxiliary steering by the motor (10) is not performed, and a normal auxiliary steering that outputs a target value as it is as a current instruction value (hereinafter simply referred to as an instruction value). Regardless of the state and the target value, the mode is switched to an auxiliary steering force adjustment state in which the output instruction value is gradually increased or decreased.

Next, an example of the processing of the control device (14) will be described with reference to the flowcharts of FIG. 2 and FIG.

FIG. 2 shows the main processing. First, an initialization process is performed in step 101, and then a determination of a vehicle state is performed in step 102, an upper limit value (hereinafter simply referred to as an upper limit value) of a current of the motor (10) is set in step 103, and a clutch (11) is set. Control and vehicle speed sensor in step 104 (13)
It repeats processing such as vehicle speed calculation based on the output of.

The control device (14) also executes an interruption process as shown in FIG. 3 at regular intervals. That is, first, in step 201, a target value is calculated based on the output (input torque) of the torque sensor (12) and the output (vehicle speed) of the vehicle speed sensor (13). In step 202, the target value and the upper limit value are calculated. The instruction value is determined by comparison, and in step 203, the instruction value is output to the motor drive circuit (15).

In step 102 of the main processing, the state of the vehicle is determined based on the outputs of the torque sensor (12), the vehicle speed sensor (13), the motor drive circuit (15), the clutch drive circuit (16), and the like. In step 202 of the interrupt process, the target value is set to the indicated value when the target value is equal to or less than the upper limit value, and the upper limit value is set to the indicated value when the target value exceeds the upper limit value. The switching of the state of the power steering device is controlled by the main processing and the interrupt processing as described below.

A range in which the vehicle speed is smaller than a predetermined determination value (hereinafter, referred to as
When the clutch is in the low-speed range, and there is no abnormality in each section, the normal assist steering state is achieved in which the target value is output as an instruction value as it is in the state of being connected to the clutch (11). That is, at this time, in step 103 of the main processing, the upper limit is set to a value larger than the maximum possible value of the target value. For this reason, in step 202 of the interrupt processing, the target value obtained in step 201 is always smaller than the upper limit value, and the target value is output as an instruction value. Therefore, the auxiliary steering force according to the input torque and the vehicle speed is
0) is given to the steering system, and normal vehicle speed adaptation control is performed.

When a first type of abnormality (hereinafter, referred to as one type of abnormality) in each part of the power steering device, for example, an abnormality in a motor current value, a voltage drop in a power supply line, or the like occurs, the motor (10) is normally turned from the auxiliary steering state. The state is immediately switched to the non-auxiliary steering state in which the auxiliary steering is not performed. That is, at this time, in step 103 of the main processing, the upper limit value is set to 0, and the clutch (11) is immediately disconnected. As a result, the motor (10) is disconnected from the steering system, and in step 202 of the interrupt processing, the indicated value becomes 0 regardless of the target value obtained in step 201, and this is output. Therefore, when one type of abnormality occurs, the auxiliary steering force is immediately switched to zero. For this reason, even in the case of an abnormality that makes it impossible to control the auxiliary steering force, there is no possibility of malfunction and the safety is extremely high.

In each part of the power steering device, a second type of abnormality (hereinafter referred to as two types of abnormality), for example, a torque sensor (1
2) When the abnormality of the vehicle speed sensor (13) occurs, or when the vehicle speed is increased from a low speed range to a range larger than a predetermined judgment value (hereinafter, referred to as a high speed range). The state is switched from the normal auxiliary steering state to the non-auxiliary steering state through the auxiliary steering force adjustment state in which the auxiliary steering force gradually decreases. That is, at this time, the upper limit is reduced each time step 103 of the main processing is executed, and the upper limit is linearly reduced from a predetermined value to 0 as shown by a chain line in FIG. Therefore, step 20 of the interrupt processing
Even if the target value obtained in step 1 changes as shown by the broken line in the figure, the indicated value is suppressed to the lower limit or less as shown by the solid line in the figure. When the upper limit decreases to 0, the clutch (11) is disengaged, and the motor (10)
Is disconnected from the steering system. As described above, when two kinds of abnormalities occur or when the speed is increased, the clutch (11) is disengaged after the auxiliary steering force is gradually changed to 0, so that the auxiliary force for disengaging the clutch (11) is reduced. Changes in steering force are small. Therefore, the discomfort given to the driver is small, and no danger is caused.

When the vehicle speed is reduced from the high speed range to the low speed range, the vehicle is switched from the non-auxiliary steering state to the normal auxiliary steering state via the auxiliary steering force adjustment state in which the auxiliary steering force gradually increases. That is, at this time, first, in step 103 of the main processing, the clutch (11) is connected, the motor (10) is connected to the steering system, and the upper limit value is increased each time step 103 is executed. As shown by a chain line, the upper limit is linearly increased from 0 to a predetermined value. For this reason, even if the target value obtained in step 201 of the interrupt processing changes as shown by the broken line in FIG.
As shown by the solid line in the figure, the temperature is suppressed to the upper limit value that gradually increases. Thus, when deceleration is performed,
Since the auxiliary steering force is gradually changed from 0 to a predetermined value after the clutch (11) is connected, the change in the auxiliary steering force when the clutch (11) is connected is small. Therefore, the discomfort given to the driver is small, and no danger is caused.

In step 103 of the main processing, only the upper limit value is gradually changed as necessary.
In 2, it is only necessary to compare the upper limit value and the target value and replace them if necessary, so that there is no need for multiplication. Therefore, there is no need to lengthen the time until the output of the current instruction value to the motor (10) and the sampling cycle, and the oscillation of the steering system can be suppressed. Since the microcomputer (17) of the control device (14) does not require a multiplication function, an inexpensive and high-performance electric power steering device can be obtained without using a high-performance microcomputer. .

Effects of the Invention According to the first invention, in the assist steering force adjustment state,
Since the command value of the current output from the control device does not exceed the upper limit value that gradually decreases or increases, the auxiliary steering force gradually decreases or increases, and does not suddenly change. For this reason, the discomfort given to the driver is small, and there is no danger.

According to the second invention, in the assist steering force adjustment state,
Since the command value of the current outputted from the control device does not exceed the gradually decreasing upper limit value, the auxiliary steering force gradually decreases and does not suddenly change. For this reason, the discomfort given to the driver is small, and there is no danger.

Also, in any of the first and second inventions, the control device does not require multiplication, so that it is not necessary to lengthen the time until the output of the current instruction value to the motor and the sampling period, and the oscillation of the steering system is reduced. Can be suppressed. Since the microcomputer of the control device does not require a multiplication function, an inexpensive and high-performance electric power steering device can be obtained without using a high-performance microcomputer.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an electric power steering device showing one embodiment of the present invention, FIG. 2 is a flowchart showing one example of main processing of a control device, and FIG. Flow chart showing examples, FIG. 4 and FIG.
The graph is a graph showing changes in the target value, the upper limit value, and the instruction value of the motor current in the assist steering force adjustment state. (10) ... electric motor, (12) ... torque sensor, (1
4) Control device.

Claims (2)

(57) [Claims] 1. A non-auxiliary steering state in which an electric motor does not perform auxiliary steering, and a current target which determines a current value of an electric motor for applying an auxiliary steering force to a steering system based on at least an input torque of a steering shaft. Control of the electric power steering device which is switched to a normal auxiliary steering state in which the value is output as the current instruction value as it is and an auxiliary steering force adjustment state in which the instruction value of the output current is gradually increased or decreased regardless of the target value of the current. In the auxiliary steering force adjustment state, an upper limit value of a current instruction value is determined, and when the vehicle speed becomes higher than a predetermined value, the upper limit value is gradually reduced, and the vehicle speed becomes lower than the predetermined value. When the target value of the current is equal to or less than the upper limit, the target value is output as the indicated value, and the target value of the current is set to the upper limit. A control device for an electric power steering device, wherein an upper limit value is output as an instruction value when the value exceeds the value. 2. A target value of a current of an electric motor for applying an auxiliary steering force to a steering system is determined based on outputs of a torque sensor for detecting an input torque of a steering shaft and a vehicle speed sensor for detecting a vehicle speed. A non-auxiliary steering state in which auxiliary steering is not performed, a normal auxiliary steering state in which the current target value is output as it is as a current instruction value, and an auxiliary steering force adjustment in which the current instruction value to be output is gradually reduced regardless of the current target value. A control device for an electric power steering device that is switched to a state, wherein in an auxiliary steering force adjustment state, an upper limit value of a current instruction value is determined, and when an abnormality occurs in the sensor, the upper limit value is gradually reduced. If the current target value is lower than the upper limit, the target value is output as the indicated value.If the current target value exceeds the upper limit, the upper limit is output. Is output as an instruction value. 2. A control device for an electric power steering device, comprising: