JPH0781590A - Electric power steering device - Google Patents

Abstract

PURPOSE:To prevent the rapid increase of the necessary steering force and the rapid change of the steerability of a vehicle even when abnormalities are generated in a power steering device and the power assist is stopped. CONSTITUTION:An electric power steering device controls a motor M1 by a control device according to the steering condition to be detected by a steering condition detecting device M2. The control device is provided with a motor driving order value operating circuit M4, a driving circuit M5, a voltage gradually dropping circuit M6, an abnormality detecting device M7, and a switching device M8. In the normal operation, the command value operating circuit, the driving circuit and the voltage gradually dropping circuit are connected to each other to prevent the gradual drop of the voltage of the voltage gradually dropping circuit. On the other hand, when abnormalities are generated, the command value operating circuit, the driving circuit and the voltage gradually dropping circuits are disconnected, and the driving circuit and the voltage gradually dropping circuit are connected to each other, and the voltage gradually dropping circuit gradually drops the voltage to the driving circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for vehicles such as automobiles, and more particularly to an electric power steering device.

[0002]

2. Description of the Related Art Conventionally, an electric power steering system for a vehicle such as an automobile generally has a motor for generating a steering assist force, a steering state detecting means for detecting a steering state of the vehicle, and a steering state detecting means for detecting the steering state. And a control device for controlling the steering assist force by controlling the motor.

As one of such electric power steering devices, for example, as disclosed in Japanese Patent Laid-Open No. 62-286874, the control device is provided with a microcomputer circuit for performing auxiliary steering control in a soft processing mode and a hardware processing mode. And an analog circuit that performs auxiliary steering control by means of an electric motor configured to continue the control by the analog circuit when an abnormality occurs in the control by the microcomputer circuit and immediately stop the auxiliary steering when an abnormality occurs in the power steering device. Power steering devices have been known for some time.

According to the electric power steering apparatus as described above, when an abnormality occurs in the power steering apparatus, the power assist is stopped, so it is certain that the motor is improperly controlled and the power assist is improperly performed. To be prevented.

[0005]

However, in the conventional electric power steering system as described above, when an abnormality occurs in the power steering system during steering, the steering assist force is sharply reduced, and therefore the vehicle There is a problem that the steering force required by the driver increases rapidly and the steerability of the vehicle changes rapidly.

In view of the above-mentioned problems in the conventional electric power steering apparatus, the present invention drastically increases the necessary steering force even when an abnormality occurs in the power steering apparatus and the power assist is stopped. An object of the present invention is to provide an electric power steering device improved so that the steerability of the vehicle does not suddenly change.

[0007]

According to the present invention, as described above, the above object is to provide a motor M1 for generating a steering assist force and a steering state detection for detecting a steering state of a vehicle, as shown in FIG. An electric power steering apparatus having means M2 and control means M3 for controlling the steering assist force by controlling the motor according to the detected steering state, the control means being the motor drive command value calculation circuit M.
4, a motor drive circuit M5, a voltage gradual decrease circuit M6, an abnormality detecting means M7 for detecting an abnormality in the power steering device, the command value calculation circuit, the drive circuit and the voltage gradual decrease circuit. A first switching state for preventing the gradual voltage reduction of the voltage gradual reduction circuit, disconnecting the command value calculation circuit, the drive circuit and the voltage gradual reduction circuit and connecting the drive circuit and the voltage gradual reduction circuit to the voltage And a switching means M8 for switching to a second switching state that allows the voltage of the gradual reduction circuit to be gradually reduced. The switching means normally maintains the first switching state, and when an abnormality is detected by the abnormality detecting means. This is achieved by an electric power steering device configured to switch to the second switching state.

[0008]

According to the above construction, when the power steering device is normal, the switching means M8 maintains the first switching state, and the command value calculation circuit M4 and the drive circuit M5.
And the voltage gradual reduction circuit M6 are connected and the voltage gradual reduction of the voltage gradual reduction circuit is blocked, so that the motor M is driven by the drive circuit.
A drive current corresponding to the command value from the command value calculation circuit is supplied to 1, and thereby the steering assist force is controlled according to the steering state.

On the other hand, when an abnormality occurs in the power steering device, the abnormality is detected by the abnormality detecting means M7, and the switching means M8 is switched to the second switching state, whereby the command value calculating circuit, the drive circuit, and The voltage gradual reduction circuit is cut off and the drive circuit and the voltage gradual reduction circuit are connected to allow the voltage gradual reduction of the voltage gradual reduction circuit, whereby the command value voltage for the drive circuit is gradually reduced. Therefore, the drive current supplied from the drive circuit to the motor M1 is also gradually reduced, and the steering assist force is gradually reduced, whereby the necessary steering force is suddenly increased and the steerability of the vehicle is suddenly changed. To be prevented.

[0010]

[Supplementary Explanation of Means for Solving the Problem] As a method of preventing a sudden change in the steering assist force when the electric power steering device is switched to the manual steering device, an abnormality detecting means is provided in the power steering device. A method of gradually reducing the motor drive command value calculated by the motor drive command value calculation circuit when it is detected that an abnormality has occurred is also conceivable. However, in this method, it is impossible to avoid a sudden change in the steering assist force when an abnormality occurs in the drive command calculation circuit itself.

According to one embodiment of the present invention, the abnormality detecting means detects at least an abnormality in the drive command value calculation circuit, and when the abnormality occurs in the command value calculation circuit, the switching means is placed in the second switching state. It is configured to switch. According to such a configuration, even if an abnormality occurs in the command value calculation circuit itself, the command voltage for the drive circuit is gradually reduced by the voltage gradual reduction circuit, whereby the drive current supplied from the drive circuit to the motor is gradually reduced. As a result, the steering assist force is gradually reduced.

[0012]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic structural view showing a first embodiment of the electric power steering apparatus according to the present invention, and FIG. 3 is shown in FIG.
3 is a block diagram showing an electronic control device shown in FIG.

In FIG. 2, reference numeral 10 denotes a steering wheel. The steering wheel 10 drives a rack bar 16 via a steering shaft 12 and a steering gear box 14. A power unit 20 is drivingly connected to the steering shaft 12 by a gear reduction mechanism 18. The power unit 20 has a motor 22 and an electromagnetic clutch 24 for selectively drivingly connecting the gear reduction mechanism 18 and the motor 22.

In the illustrated embodiment, the steering shaft 12 has a torque sensor 26 for detecting a steering torque T.
Is provided, and the output of the torque sensor is supplied to the electronic control unit 28. A signal indicating the vehicle speed V detected by the vehicle speed sensor 30 is also input to the electronic control unit 28.

As shown in detail in FIG. 3, electronic controller 28 includes a microcomputer 32, which is a central processing unit (CPU) 34.
A read only memory (ROM) 36, a random access memory (RAM) 38, and an input / output port device 40.
And they are connected to each other by a bidirectional common bus 42. A signal indicating the steering torque T detected by the torque sensor 26 and a signal indicating the vehicle speed V detected by the vehicle speed sensor 30 are input to the input / output port device 40. The input / output port device 40 appropriately processes the signal input thereto, and outputs the processed signal to the CPU and the RAM 38 according to the instruction of the CPU 34 based on the control program stored in the ROM 36.

The ROM 36 stores the control program shown in FIG. 4 and maps corresponding to the graphs shown in FIGS. 5 and 6. The CPU 34 is configured to perform various calculations and signal processing based on the control program shown in FIG. 4, as will be described later. The input / output port device 40 is the CPU 3
D / A converter 44 and drive circuit 46
The control signal is output to the motor 22 via the D / A converter 48 and the drive circuit 50, and the control signal is output to the electromagnetic clutch 24.

An integrating circuit 52 as a voltage gradual decreasing circuit is provided between the D / A converter 44 and the drive circuit 46. Conduction between the integrating circuit 52 and the D / A converter 44 and the driving circuit 46 is performed by two analog switches 54 and 56.
It is controlled by. The switch 54 switches between a first position where the resistor side terminal of the integrating circuit 52 and the D / A converter 44 are connected, and a second position where the resistor side terminal of the integrating circuit is grounded as shown. It is like this. Further, the switch 56 is switched between a first position where the D / A converter 44 and the drive circuit 46 are connected, and a second position where the capacitor side terminal of the integration circuit 52 and the drive circuit 46 are connected, as shown in the figure. It is like this.

The switching of the two switches 54 and 56 is controlled by a signal from a watchdog timer 58 as shown. Watchdog timer 5
8 detects whether the operation of the CPU 34 is normal, and C
When the operation of the PU is normal, the high signal is output to maintain the switches 54 and 56 in the first position, and when the operation of the CPU is abnormal, the low signal is output to output the switch 5
It is adapted to switch 4 and 56 to the second position.
When the output of the watchdog timer 58 is a low signal, a warning lamp 60 is turned on via a relay not shown in the figure, which alerts the driver of the vehicle that an abnormality has occurred in the power steering device. It is supposed to emit.

Thus, the integrating circuit 52 has two switches 5
When 4 and 56 are in the first position, the capacitor is charged with the voltage according to the command voltage to the drive circuit 46,
When the two switches are in the second position, they form a voltage gradual decrease means for gradually decreasing the voltage by discharging the electric charge charged in the capacitor through the resistor. The two switches 54 and 56 connect the microcomputer 32 as a motor drive command value calculating circuit to the drive circuit 46 and the integrating circuit 52 and prevent the voltage from gradually decreasing in the integrating circuit. 32 to disconnect the drive circuit 46 and the integration circuit 52 from each other and drive circuit 46
And an integrating circuit 52 are connected to each other to constitute a switching means for switching to a second switching state in which the voltage of the integrating circuit is gradually reduced.

Next, the power assist control in the first embodiment will be described with reference to the flow chart shown in FIG. The control by the electronic control unit 32 is started by closing an ignition switch not shown in FIG.

First, in step 10, the control signal is output to the electromagnetic clutch 24 via the drive circuit 50 so that the clutch is engaged. In step 20, the steering torque T detected by the torque sensor 26 is shown. The signal and the signal indicating the vehicle speed V detected by the vehicle speed sensor 30 are read.

In step 30, the basic assist amount Tab is calculated from the map corresponding to the graph shown in FIG. 5 based on the steering torque T read in step 20.
In step 40, the vehicle speed coefficient Kv is calculated from the map corresponding to the graph shown in FIG. 6 based on the vehicle speed V read in step 20, and in step 50, the vehicle speed coefficient Kv is calculated in accordance with the following equation 1 The basic assist amount Tab calculated in step S40 and the vehicle speed coefficient Kv calculated in step S40
The assist amount Ta is calculated as the product of

[Equation 1] Ta = Tab · Kv

At step 60, the control signal corresponding to the assist amount Ta calculated at step 50 is D / A.
By being output to the motor 22 via the converter 44 and the drive circuit 46, the steering assist force is increased by the assist amount Ta.
Is controlled to a value corresponding to, and then the process returns to step 20.

The power assist control itself according to the flowchart shown in FIG. 4 does not form the subject matter of the present invention, and the power assist control may be performed in any manner as long as the steering assist force is calculated at least according to the steering torque. May be performed.

Thus, according to the illustrated first embodiment, when the CPU 34 of the microcomputer 32 is operating normally, the output of the watchdog timer 58 is a high signal and the two switches 54 and 56 are in the first state. And the D / A converter 44 and the drive circuit 46 are maintained in a conductive state. Then, in step 30, the basic assist amount Tab is calculated from the map corresponding to the graph shown in FIG. 5, and in step 40 the vehicle speed coefficient Kv is calculated from the map corresponding to the graph shown in FIG. In step 50, the assist amount Ta is the basic assist amount Tab
Is calculated as the product of the vehicle speed coefficient Kv and a control signal corresponding to the assist amount Ta is output to the motor 22 in step 60, whereby the steering assist force corresponds to the steering torque and becomes lower as the vehicle speed becomes higher. Since it is controlled, a light steering is ensured in a low vehicle speed range, and a good steering stability is ensured in a high vehicle speed range.

On the other hand, C of the microcomputer 32
When an abnormality occurs in the operation of the PU 34, the output of the watchdog timer 58 becomes a low signal, the two switches 54 and 56 are switched to the second position, and the D / A converter 4
4 and the drive circuit 46 are disconnected from each other and the integration circuit 52 is grounded. Therefore, the command voltage to the drive circuit 46 gradually decreases as shown in FIG. 7, and thereby the voltage of the control current output to the motor 22 also gradually decreases,
Eventually the power assist will be stopped.

FIG. 8 is a block diagram showing an electronic control unit in a second embodiment of the electric power steering system according to the present invention. It should be noted that in FIG. 8, portions corresponding to the portions shown in FIG. 3 are given the same reference numerals as those given in FIG.

In this embodiment, the D / A converter 4
4 is provided between the drive circuit 46 and the drive circuit 46, and the integration circuit 52 is always connected to the drive circuit 46 at its capacitor-side terminal. The switch device 62 controls the conduction between the D / A converter 44 and the drive circuit 46 and the grounding of the resistor-side terminal of the integrating circuit 52. In the illustrated embodiment, two switches 64 and It is a double switch composed of 66.

The switch 64 is switched between a closed position for connecting the D / A converter 44 and the drive circuit 46 and an open position for interrupting the conduction between them as shown in the figure, and a switch 66 is for the resistor side of the integrating circuit 52. The terminal is switched between an open position for blocking the grounding of the terminal and a closed position for grounding the terminal. Watchdog timer 5 opens and closes these switches.
When the output of the watchdog timer 58 is a high signal, the switches 64 and 66 are maintained in the closed position and the open position, respectively, and when the signal from the watchdog timer becomes a low signal, the switch 6 is controlled.
4 and 66 are adapted to be switched between an open position and a closed position, respectively.

Therefore, also in the second embodiment, when the CPU 34 of the microcomputer 32 is operating normally, the output of the watchdog timer 58 is a high signal, so that the switch 64 is maintained in the closed position. 66 is maintained in the open position, and the D / A converter 44 and the drive circuit 46 are maintained in a conductive state, whereby the required power assist control is executed.

On the other hand, C of the microcomputer 32
When an abnormality occurs in the operation of the PU 34, the output of the watchdog timer 58 becomes a low signal, the switch 64 is switched to the open position, the switch 66 is switched to the closed position, and the D / A
The electrical connection between the converter 44 and the drive circuit 46 is cut off, and the integration circuit 52 is grounded.
Is gradually reduced, and the voltage of the control current output to the motor 22 is gradually reduced.

Although the present invention has been described in detail above with reference to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art that it is possible.

For example, in each of the above-described embodiments, the abnormality of the CPU 34 of the microcomputer 32 is detected by the watchdog timer 58, and when the abnormality occurs in the CPU, the integrating circuit 52 is grounded, so that the command voltage to the drive circuit 46 is given. However, the switches 54 and 56, 64 and 66 are switched in response to the detection of the abnormality by the abnormality detecting means which also detects the abnormality of the portion other than the CPU 34 of the electric power steering apparatus. The opening and closing may be controlled.

In each of the above-described embodiments, the command voltage for the drive circuit 46 is gradually reduced by grounding the integrating circuit 52 only when the CPU 34 of the microcomputer is abnormal. But CP
Regarding an abnormality other than U, for example, as described in Japanese Patent Application No. 5-123622 and the drawings by the same applicant as the applicant of the present application, the abnormality is detected by the arithmetic processing by the microcomputer 32 and a response to the abnormality detection is made. Then C
The PU may be configured such that the command voltage to the motor drive circuit is gradually reduced.

Further, in each of the illustrated embodiments, the voltage gradual reduction means is the integration circuit 52, but the voltage gradual reduction circuit gradually reduces the command voltage to the drive circuit when an abnormality occurs in the motor drive command value calculation circuit. It may have any configuration as long as it is obtained.

[0037]

As is apparent from the above description, according to the present invention, when an abnormality occurs in the power steering device, the abnormality is detected by the abnormality detecting means M7, and the switching means M8 is in the second switching state. Switching to the command value calculation circuit, the drive circuit and the voltage gradual decrease circuit are disconnected, and the drive circuit and the voltage gradual decrease circuit are connected to allow the voltage gradual decrease of the voltage gradual decrease circuit. Is gradually reduced, and accordingly, the drive current supplied from the drive circuit to the motor M1 is also gradually reduced.
The steering assist force is gradually reduced, whereby it is possible to reliably prevent the necessary steering force from rapidly increasing and the steerability of the vehicle from changing rapidly.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an electric power steering device according to the present invention in correspondence with the description of the claims.

FIG. 2 is a schematic configuration diagram showing a first embodiment of an electric power steering device according to the present invention.

FIG. 3 is a block diagram showing the electronic control device shown in FIG. 2.

FIG. 4 is a flowchart showing a power assist control routine achieved by the electronic control device shown in FIGS. 2 and 3.

FIG. 5 is a graph showing a relationship between a steering torque T detected by a torque sensor and a basic assist amount Tab.

FIG. 6 is a graph showing a relationship between a vehicle speed V detected by a vehicle speed sensor and a vehicle speed coefficient Kv.

FIG. 7: CPU of electronic control unit microcomputer
5 is a graph showing an example of changes in the command voltage for the drive circuit when an abnormality occurs in the drive circuit.

FIG. 8 is a block diagram showing an electronic control device of a second embodiment of the electric power steering device according to the present invention.

[Explanation of symbols]

 10 ... Steering wheel 12 ... Steering shaft 14 ... Steering gear box 16 ... Rack bar 22 ... Motor 24 ... Electromagnetic clutch 26 ... Torque sensor 28 ... Electronic control unit 30 ... Vehicle speed sensor 32 ... Microcomputer 52 ... Integration circuits 54, 56 ... Switch 58 ... Watchdog timer 60 ... Warning lamp 64, 66 ... Switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nao Iwasaki 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Masaaki Tsuboi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation

Claims (1)

[Claims] 1. A motor for generating a steering assist force, a steering state detecting means for detecting a steering state of a vehicle, and a control means for controlling the steering assist force by controlling the motor according to the detected steering state. An electric power steering device having: a control circuit for controlling a motor drive command value; a motor drive circuit;
An abnormality detecting means for detecting an abnormality in the power steering device, a first switching state for connecting the command value calculation circuit, the drive circuit and the voltage gradual reduction circuit and preventing the voltage gradual reduction of the voltage gradual reduction circuit. Switching to a second switching state in which the command value calculation circuit, the drive circuit and the voltage gradual reduction circuit are disconnected and the drive circuit and the voltage gradual reduction circuit are connected to allow the voltage gradual reduction of the voltage gradual reduction circuit. Switching means, and the switching means is configured to normally maintain the first switching state and switch to the second switching state when an abnormality is detected by the abnormality detecting means. An electric power steering device.