JPH04252775A - Electric power steering device - Google Patents

Abstract

PURPOSE:To prevent sudden increase of steering resistance at generation of abnormality in a steering torque sensor and give the operator enough composure to cope with generation of the abnormality, in an electric motor-driven power steering device. CONSTITUTION:When abnormality in a main steering torque sensor 9A is detected (step 3c), the drive current of an electric motor to generate steering subsidiary torque is decided based on the steering torque detected value from a subsidiary steering torque sensor 9B (step 3d1-3d4), and when abnormality is also detected in the subsidiary steering sensor 9B, a motor current setting value IM against a motor drive circuit is gradually decreased (step 3a), by decreasing the steering subsidiary torque value T calculated based on the direct before steering torque detected value a gradually decreasing value DELTAT a time.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an electric power steering device in which the steering force of a vehicle is assisted by the torque generated by an electric motor, and is particularly suitable for application to industrial vehicles such as heavy-load battery forklifts. It is something.

0002

2. Description of the Related Art Conventional electric power steering devices for industrial vehicles include, for example,
Some of them are described in Japanese Patent No. 146736. This conventional example is an abnormality detection device for a torque detector used in an electric power steering device, which determines whether the output voltage of the torque detector is within a predetermined setting range, and determines whether or not the output voltage of the torque detector is within a predetermined setting range. an output voltage abnormality detection circuit that determines that the torque detector is disconnected and outputs an abnormal state detection signal when the voltage is lower than a certain reference value; The output voltage abnormality detection circuit and the applied voltage abnormality detection circuit detect abnormalities such as disconnections and short circuits in the torque detector. When detected, the power supply to the motor drive circuit that drives the motor is immediately cut off, and the input of a control signal to the motor drive circuit is cut off.

0003

[Problems to be Solved by the Invention] However, in the above-mentioned conventional electric power steering device for industrial vehicles, when the torque detector is in an abnormal state such as disconnection or short circuit, the power supply to the electric motor is immediately turned off. By cutting off the supply and stopping the generation of steering assist force by the electric motor, the elastic deformation of the steering system, such as tire deflection, which had previously been caused by the torque of the electric motor, is temporarily released, and this causes the steering Since the transmission is transmitted to the wheels, there is a problem in that a large kickback occurs in the steering wheel, giving a shock to the driver operating the steering wheel. In particular, electric power steering devices for battery forklifts have a much larger steering assist force from the electric motor of the power steering device than that for passenger cars, and under normal conditions they rely only on the steering assist force of the electric motor. As a result, the above-mentioned kickback becomes large and the shock felt by the driver becomes large.At the same time, the steering assist force from the electric motor suddenly drops to zero, and the steering resistance of the steering wheel increases rapidly. There is a problem in that because the driver recognizes the occurrence of an abnormality due to the sudden increase in the number of abnormalities, there is little leeway to perform operations such as stopping the vehicle to deal with the occurrence of the abnormality.

SUMMARY OF THE INVENTION Therefore, an object of the present invention has been made in view of the above-mentioned problems of the conventional example. An electric power steering system that can solve the above-mentioned problems of the conventional example by gradually decreasing the steering torque, or by controlling the electric motor based on the steering torque detection value of another normal steering torque detector. The goal is to provide equipment.

[0005]

[Means for Solving the Problems] In order to solve the problems of the conventional example, an electric power steering device according to a first aspect detects the steering torque of the steering system, as shown in the diagram corresponding to the claims in FIG. An electric power steering device comprising: a steering torque detecting means for detecting a steering torque; and a control means for controlling an electric motor that generates a steering assist force for the steering system based on a steering torque detection value of the steering torque detecting means. , comprising an abnormality detection means for detecting an abnormal state of the steering torque detection means and outputting an abnormality detection signal, and the control means is configured to detect an abnormality in the electric motor when receiving an abnormality detection signal from the abnormality detection means. It has a torque gradual reduction means for gradually reducing the steering assist torque.

Further, the electric power steering device according to claim 2 includes a steering torque detection means for detecting the steering torque of the steering system, and a steering torque detection means for detecting the steering torque of the steering torque detection means, as shown in the diagram corresponding to the claim in FIG. In an electric power steering apparatus, the electric power steering apparatus includes a control means for controlling an electric motor that generates a steering assist force for the steering system based on a detected value, and an abnormality is detected by detecting an abnormal state of the steering torque detection means. The steering torque detection means includes at least two of a main steering torque detector and an auxiliary steering torque detector.
The control means has an input for switching the input steering torque detection value from the main steering torque detector to the auxiliary steering torque detector when receiving an abnormality detection signal from the abnormality detection means. It has a switching means.

[0007]

In the electric power steering system according to the first aspect of the present invention, when an abnormal state occurs in the steering torque detecting means, an abnormal state detection signal is outputted from the abnormal state detecting means to the control means. In response to this, the control means gradually reduces, for example, the drive current to the electric motor, thereby gradually reducing the steering assist torque generated by the electric motor. As a result, kickback can be gradually eliminated, and the steering feel of the steering wheel gradually becomes heavier, allowing the driver to gradually recognize the occurrence of an abnormality and perform operations such as stopping the vehicle in response to the occurrence of an abnormality. You can have plenty of leeway.

Further, in the electric power steering system according to claim 2, at least two torque detectors, a main steering torque detector and an auxiliary steering torque detector, are provided as the steering torque detecting means, and the main steering torque is always detected. The steering torque detection value of the detector is input to the control means, the electric motor is drive-controlled based on the steering torque detection value, and when the abnormality detection means detects an abnormality in the main steering torque detector, the sub-steering By switching to the steering torque detection value of the torque detector, the normal steering assist state is continued.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the electric power steering apparatus of the present invention will be described with reference to the drawings. FIG. 3 is a schematic configuration diagram showing a first embodiment of the present invention. In the figure, reference numeral 1 denotes a steering wheel, the steering force of which is transmitted to a steering gear 3 via a steering shaft 2 to turn steered wheels.

The steering shaft 2 has a reduction gear 5.
The output shaft 7a of the electric motor 7 is connected to the electric motor 7 via the servo motor 7, and the electric motor 7 is driven and controlled by a control device 8 serving as a control means. This control device 8 includes a steering wheel 1
A steering torque detection value TS including the steering direction, which is a voltage signal of a steering torque sensor 9 composed of a potentiometer that detects the steering torque inputted to, for example, as a torsional angular displacement of a torsion bar, and a vehicle speed sensor that detects the vehicle speed of the vehicle. 10 vehicle speed detection values V are input. As shown in FIG. 4, the control device 8 includes an amplifier 11 to which the steering torque detection value TS of the steering torque sensor 9 is input, and a sensor abnormality detection circuit 1 that detects abnormality of the steering torque sensor 9.
2, the amplified output TS1 of the amplifier 11 is input to the microcomputer 16 via the A/D converter 14, and the abnormality detection signal AS of the steering torque abnormality detection circuit 12 is inputted to the microcomputer 16 via the A/D converter 14.
is directly input to the microcomputer 16, and further,
The vehicle speed detection value V of the vehicle speed sensor 10 is the interface circuit 1
A motor current set value IM is inputted to the microcomputer 16 via the microcomputer 5 and outputted from the microcomputer 16, and is supplied to a motor drive circuit 17 that outputs a drive current to the electric motor 7.

Here, the amplifier circuit 11 outputs an amplified output TS1 (=βTS) obtained by multiplying the input steering torque detection value TS by a coefficient β corresponding to a predetermined amplification factor. Further, the steering torque abnormality detection circuit 12 includes a steering torque sensor 9
an applied voltage abnormality detection circuit 12a that detects a short circuit abnormality by detecting an abnormality in the applied voltage applied to the steering torque sensor 9;
and an output voltage abnormality detection circuit 12b that detects an abnormality in the steering torque detection value TS outputted from the steering torque sensor 9 to detect a disconnection abnormality. When detected, a detection signal with a logical value of "1" is output to the OR gate 12c, and an abnormality detection signal AS is output from the OR gate 12c.

Furthermore, the microcomputer 16 is shown in FIG.
The calculation process is executed according to the flowchart shown in FIG. 6, and the motor drive current command value IM is calculated based on the steering torque detection value TS of the steering torque sensor 9.
Abnormal state processing is executed when an abnormality in the steering torque sensor 9 is detected. Next, the operation of the above embodiment will be explained according to the flowcharts of FIGS. 5 and 6 showing the processing procedure of the microcomputer 16.

That is, the flowchart in FIG. 5 shows a control process consisting of a main program, which is started by turning on the key switch, and first, in step (2), it is determined whether the microcomputer 16 is in a normal state or not. Determine whether This determination is made, for example, by determining whether or not the watchdog timer 18 connected to the microcomputer 16 has timed up. It is determined that this has occurred and the process moves to step (■). In this step (2), abnormality processing such as predetermined data saving is performed, and then the control processing is ended.

On the other hand, if the watchdog timer 18 has not timed up in step (2), it is determined that the microcomputer 16 is in a normal state, and the process proceeds to step (2). In this step (2), it is determined whether the steering torque sensor 9 is in an abnormal state. This determination is made by determining whether the abnormality detection signal AS output from the steering torque abnormality detection circuit 12 has a logical value of "1". Here, when the abnormality detection signal AS has the logical value "1", it is determined that the steering torque sensor 9 is abnormal, and the process moves to step ■a to execute sensor abnormality processing to be described later, and then step ■b It is determined whether the control abort flag is set to "1" or not, and when the control abort flag is set to "1", the process proceeds to step (3) and the control abort flag is set to "0". If it has been reset, the process moves to step (2) described later.

Further, if the determination result in step (2) is that the abnormality detection signal AS has a logical value of "0", the process moves to step (2). In this step (2), the steering torque detection value TS amplified by the amplifier 11 is read, and this steering torque detection value TS is set to a preset value +VL between which zero is set.
It is determined whether it is within the dead band width between and -VL. Here, when -VL≦TS≦+VL, it is determined that the detected steering torque value TS is within the dead band width, and the process returns to step (2), and TS <-VL, TS
>+VL, the process moves to step (2).

In this step (2), the steering torque detection value TS read in the step (2) is multiplied by a preset control gain KT to obtain a steering assist torque value TN (=KT
- TS ) is calculated and updated and stored in a predetermined storage area of the storage device. Next, the process moves to step (3), and it is determined whether or not the electric motor 7 is abnormal. In this determination, the drive current of the motor drive circuit 17 is detected, and it is determined whether the electric motor 7 is in an abnormal state due to a short circuit state, a disconnection state, or the like. At this time, if the electric motor 7 is in an abnormal state, the process moves to step (a) to perform electric motor abnormality processing that cuts off the power supply to the electric motor 7, and then moves to the step (2), where the electric motor 7 When the state is normal, the process moves to step (3).

In this step (2), the difference between the steering assist torque value TN calculated in step (2) and the steering assist torque value TN-1 calculated in the previous process, that is, the amount of change ΔTN is calculated.
is calculated and compared with the preset maximum amount of change ΔTNMAX. If ΔTN > ΔTNMAX, it is determined that the amount of change is excessive, and the process returns to the above step and ΔT
When ≦ΔTNMAX, the process moves to step (2).

[0018] In this step (2), the preset
The motor current setting value IM is calculated with reference to the map corresponding to the characteristic diagram showing the relationship between the steering assist torque value T and the motor current setting value IM shown in FIG.
7, and then return to step (2). On the other hand, as shown in FIG. 6, the sensor abnormality processing in step ■a first turns on a warning light installed in the instrument panel of the driver's seat in step ■a1, and then moves to step ■a2, which is not shown. A stop command for gently stopping the vehicle is output to the travel control controller that controls the travel of the vehicle, and then the process moves to step (a3).

In this step ■a3, the steering assist torque value T at the time of the previous processing stored in the steering assist torque value storage area of the storage device is read out, and then the process proceeds to step ■a4, where the steering assist torque value T is read out. Determine whether or not is zero. At this time, when T=0, the process directly goes to step ■a12 and the control stop flag is set to "1".
After setting it to , complete the sensor error processing and proceed to step ■
Move to b, and when T≠0, step ■a5
to move to.

In this step (a5), it is determined whether or not the gradual decrease value setting flag FS is set to "1", and when the flag FS is set to "1",
Move directly to step ■a8, and flag FS is “0”
If the value has been reset to , the process proceeds to step ■a6, where a gradual decrease value ΔT for gradually decreasing the steering assist torque value T is set based on the following formula (1), and then the process proceeds to step ■a7, where the gradual decrease value is set. After setting the flag FS to "1", the process moves to step (a8).

[0021]ΔT=|T|/n …………(
1) Here, n is an arbitrary variable that sets the time for gradually reducing the steering assist torque value T to zero, and if the variable n is set to a small value, the steering assist torque value T
The amount of change in the steering assist torque value T becomes larger and the gradual reduction time becomes shorter, and if it is set to a larger value, the amount of change in the steering assist torque value T becomes smaller and the gradual reduction time becomes longer.

In step (a8), it is determined whether the steering assist torque value T is positive or not, and if T>0,
Proceed to step ■a9 to determine the current steering assist torque value T.
The value obtained by subtracting the gradual decrease value ΔT set in step ■a6 from the above is calculated as a new steering assist torque value T (=T - ΔT), and this is updated and stored in the steering assist torque value storage area, and then step ■a11 If T<0, the process proceeds to step ■a10, where the value obtained by adding the gradual decrease value ΔT set in step ■a6 to the current steering assist torque value T is set as a new steering assist torque value T (= T+ΔT)
After this is updated and stored in the steering assist torque value storage area, the process moves to step (2)a11.

In step ■a11, step ■a9
Or, it is determined whether the steering assist torque value T updated in step ■a10 is within the tolerance range set by a predetermined tolerance value TA that includes zero, and if -TA≦T≦+TA, the process proceeds to step ■a12. After setting the control stop flag FC to "1", the sensor abnormality processing is terminated and the process proceeds to the next step ■b, where T<-TA or T>+TA
If so, the sensor abnormality processing is immediately terminated and the process proceeds to the next step (ii) b.

Here, the steering control process in FIG. 5 corresponds to the control means, and among these, the processes in steps ■, ■a, ■b and steps ■a1 to ■a12 in FIG. 6 correspond to the torque gradual reduction means. . Therefore, when all of the steering control system including the electric motor 7, the steering torque sensor 9, and the microcomputer 16 are in a normal state, when the steering control process shown in FIG. The process moves to step (2), and in this step (2) it is determined whether or not the steering torque detection value TS of the steering torque sensor 9 is within the dead band width. Since the steering torque detection value TS of the sensor 9 is approximately zero, the process returns to step (2), so the motor current setting value IM maintains zero, and the drive current supplied to the electric motor 7 by the motor drive circuit 17 becomes zero. Therefore, the electric motor 7 is in a stopped state.

When the steering wheel is turned to the right or left from this non-steering state, the steering torque sensor 9 outputs a detected steering torque value TS corresponding to positive or negative steering torque, which is outputted to the microcomputer 16.
5, the process moves from step (2) to step (2) to calculate the steering assist torque value T corresponding to the detected steering torque value T, and then moves to step (2) via steps (2) and (2), and the process proceeds to step (2) in FIG. The motor current setting value IM for the electric motor 7 is calculated with reference to the memory table corresponding to the memory table, and this is output to the motor drive circuit 17.

Therefore, the direction in which the electric motor 7 is energized is set depending on the positive or negative value of the motor current setting value IM inputted to the motor drive circuit 17, and a driving current corresponding to the motor current setting value IM is supplied to the electric motor 7. As a result, the electric motor 7 generates a steering assist torque corresponding to the steering of the steering wheel, as shown by the characteristic curve L shown by the solid line in FIG. 8, and this is transmitted to the steering shaft 2 via the reduction gear 5. Can perform light steering.

However, during the above-mentioned steering of the steering wheel, an abnormality such as a short circuit or disconnection occurs in the steering torque sensor 9, and this abnormality is detected by the applied voltage abnormality detection circuit 12a of the sensor abnormality detection circuit 12 and the output voltage abnormality detection circuit. 12b, the abnormality detection circuits 12a and 12b output an abnormality detection signal with a logic value of "1", and therefore, the OR gate 12c outputs an abnormality detection signal AS with a logic value of "1" to the microcomputer 16.

In this way, when the abnormality detection signal AS with the logical value "1" is input to the microcomputer 16, as shown in FIG.
In the process, the process moves from step (2) to step (2) a, and the sensor abnormality process shown in FIG. 6 is executed. Therefore, a warning light indicating that a sensor error has occurred is lit (
Step (a1), then a travel stop command is output to the travel controller to gently stop the vehicle from traveling (step (a2)).

Next, the previous steering assist torque value T is read out (step ①a3). At this time, as shown in FIG.
Assuming that an abnormal state occurs in the steering torque sensor 9 at time t1 while the steering wheel is returning from the right steering state to the neutral state, the previous steering assist torque value T
is +T1 as shown in Figure 8, and +T1
>0, so step ■a4 to step ■a5
Since the gradual decrease value setting flag FS has been reset to "0", the process moves to step ■a6 and the above (
1) Calculate the gradual decrease value ΔT according to the formula.

Next, in step ■a7, the gradual decrease value setting flag FS is set to "1", and then in step ■a8
After that, the process moves to step ■a9, where the gradual decrease value ΔT is subtracted from the current steering assist torque value T to calculate a new steering assist torque value T, which is updated and stored in the steering assist torque storage area, and then step ■ The process moves to a11, and since T>+TL, the sensor abnormality processing is terminated and the process proceeds to step ■b in Fig. 5.
Since the control stop flag has been reset to "0", the process moves to step (2) and calculates the motor current setting value IM based on the updated and stored steering assist torque value T, as in the normal state. and outputs it to the motor drive circuit 17. At this time, as described above, since the steering assist torque value T is decreased by the gradual decrease value ΔT, the motor current set value IM is also reduced by this amount, and the steering assist torque generated by the electric motor 7 is also reduced.

Thereafter, the process returns from step (2) to step (2), and if the abnormal state of the steering torque sensor 9 continues, the process moves from step (2) to step (2) a to re-execute the sensor abnormality process. At this time, in the sensor abnormality processing shown in FIG. 6, when moving from step ■a4 to step ■a5, the gradual decrease value setting flag FS is set to "1" during the previous processing.
”, the steering assist torque value T is gradually decreased based on the previously calculated gradual decrease value ΔT without changing the gradual decrease value ΔT. As a result, the steering assist torque value T is gradually decreased as shown by the broken line in FIG. The assist torque value T gradually decreases, and the steering assist torque generated by the electric motor 7 gradually decreases accordingly.

Then, by repeating the above processing, when the steering assist torque value T becomes equal to or less than the set value +TA, in the sensor abnormality processing shown in FIG.
After the process moves to a12 and the control stop flag FC is set to "1", the process moves to step (2) b. Therefore, the process moves from step (2)b to step (2) to end the steering control process, cut off the power supply to the electric motor 7, and end the control.

[0033] Furthermore, the abnormal state of the steering torque sensor 9 is
When the occurrence occurs at time t2 in FIG. 8, the immediately preceding steering assist torque value T is -T2, so when the sensor abnormality processing in FIG. 5 is executed, the process moves from step ■a8 to step ■a10. By adding the gradual decrease value ΔT to the previous steering assist torque value T, the steering assist torque value T
is gradually reduced as shown by the broken line in FIG. 8, and the steering assist torque generated by the electric motor 7 for left steering is reduced.

Furthermore, when the abnormal state of the steering torque sensor 9 occurs when the steering assist torque value T is zero, when the sensor abnormality processing of FIG. Since the control control flag FC is set to "1" in step (2), when the next step (2) b is processed, the control is directly transferred to step (2) and the control is immediately stopped. This is because when the steering assist torque value T is zero, the steering wheel is in a neutral state and the electric motor 7 is in a stopped state, so there is no need to perform the above-mentioned gradual reduction process.

As described above, according to the first embodiment, when the steering torque sensor 9 is in an abnormal state such as short circuit or disconnection, the gradual reduction process is performed based on the immediately previous steering assist torque value T. By doing this, the steering assist torque generated by the electric motor 7 is gradually reduced, and the amount of elastic deformation of the steering system due to the steering assist torque generated by the electric motor 7 is also gradually reduced, thereby reducing kickback. In addition, since the steering resistance of the steering wheel gradually increases, the driver can be gradually made aware of the occurrence of an abnormality, and can perform operations such as stopping the vehicle with sufficient time to prevent the occurrence of an abnormality. be able to. In addition, since the gradual decrease value ΔT is calculated according to equation (1) based on the steering assist torque value T immediately before the steering torque sensor 9 becomes abnormal, as shown in FIG. Even if the steering assist torque value T is different, the steering assist torque value T can always be made zero within a certain period of time. Here, the time required for the steering assist torque value T to become zero is preferably approximately 3 to 5 seconds.

In the first embodiment, when an abnormality occurs in the steering torque sensor 9, the immediately preceding steering assist torque value T
We have described the case where the gradual decrease value ΔT is calculated based on
The gradual decrease value ΔT may be set to a preset constant value regardless of the immediately preceding steering assist torque value T. Further, in the first embodiment, a case has been described in which the steering assist torque value T is changed stepwise, but it may be changed to a hyperbolic characteristic or the like to perform a continuous gradual reduction process.

Furthermore, in the first embodiment, the case where the electric motor 7 is directly connected to the steering shaft 2 via the reduction gear 8 has been described, but the output shaft of the electric motor 7 and the input shaft of the reduction gear 8 are An electromagnetic clutch may be provided between the two, and the engagement force of the electromagnetic clutch may be gradually reduced to gradually reduce the steering assist torque generated by the electric motor.

Next, a second embodiment of the present invention will be described with reference to FIGS. 10 and 11. In this second embodiment, as shown in FIG. 10, two sensors, a main steering torque sensor 9A and an auxiliary steering torque sensor 9B, are provided as steering torque detection means, and each of these sensors 9A and 9B has a sensor abnormality. In addition to providing detection circuits 12A and 12B, each sensor 9A,
Steering torque detection values TSA and TSB outputted from the analog selector switch 2 select one of the amplified outputs of the amplifiers 11A and 11B in accordance with a selection signal from the microcomputer 16 via the amplifiers 11A and 11B.
0, and the detected steering torque value selected by the analog changeover switch 20 is input to the microcomputer 16 via the A/D converter 14, and the microcomputer 16 corresponds to that shown in FIG. This embodiment has the same configuration as the first embodiment described above, except that the process shown in FIG. 11 is executed, and the same parts as in the first embodiment are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In other words, the steering control process in FIG.
The determination process in step (3) in the steering control process reads the abnormality detection signal ASA of the sensor abnormality detection circuit 12A,
This is replaced with a process of determining whether or not the logical value is "1", and when the determination result is the logical value "0", it is determined that the main steering torque sensor 9A is in a normal state, and the step When the logical value is "1", the process moves to step d1.

In step (d1), it is determined whether or not the auxiliary steering torque sensor 9B is abnormal. This determination is made by reading the abnormality detection signal ASB of the sensor abnormality detection circuit 12B and determining whether or not this is the logical value "1". Here, the abnormality detection signal ASB has a logical value of “0”.
”, it is determined that the auxiliary steering torque sensor 9B is in a normal state, and the process proceeds to step d2.

In this step d2, the control gain KT necessary for the arithmetic processing in step 2 mentioned above is set to KT/
n, then proceed to step d3, and change the reading of the detected steering torque value in step 2 from the detected steering torque value TSA of the main steering torque sensor 9A to the detected steering torque value TSB of the auxiliary steering torque sensor 9B. A selection signal with a logical value of "1" for the purpose of After that, move on to step ■.

Further, when the determination result in step ■d1 is that the abnormality detection signal ASB is a logical value "1", it is determined that the auxiliary steering torque sensor 9B is also in an abnormal state, and the sensor abnormality in step ■a is detected. Shifting to processing, the above-described sensor abnormality processing in FIG. 6 is executed, and then step
The process moves to step e, where the warning light 21 is controlled to be turned on, and then the process moves to step 2b.

The process shown in FIG. 11 corresponds to the control means, and among these, the process at step d3 corresponds to the input switching means. Therefore, when the main steering torque sensor 9A is in a normal state, by directly moving from step (c) to step (2), the sensor state display warning light 21 remains in the off state, similar to the first embodiment described above. Executes steering control processing during normal operation.

However, if an abnormal condition occurs in the main steering torque sensor 9A, steps ■c to step ■d
1, and when the auxiliary steering torque sensor 9B is normal, the control gain KT is reduced to 1/of the normal state of the main steering torque sensor 9A by moving to step d2.
At the same time, the logical value is set to "1" at step d3.
” is output to the analog changeover switch 20, and control is performed to read the normal steering torque detection value TSB of the auxiliary steering torque sensor 9B in place of the steering torque detection value TSA of the main steering torque sensor 9A that has become abnormal. Further, in step (d4), the warning light 21 flashes to warn of the abnormal state of the main steering torque sensor 9B.

In this way, by reducing the control gain KT to 1/n of the normal value, the steering assist torque value T calculated in step (2) becomes 1/n of the normal value, and accordingly, step (2) Motor current command value IM calculated by
is a smaller value than when the main steering torque sensor 9A is normal, so the steering assist torque generated by the electric motor 7 is proportional to the steering torque detection value TSB, but it is a smaller value than when the main steering torque sensor 9A is normal. The steering feeling of the wheel becomes heavier than when it is normal. Therefore, the abnormal state of the main steering torque sensor 9A can be directly recognized by the driver by increasing the steering feeling of the steering wheel.

Further, when both the main and auxiliary steering torque sensors 9A and 9B are in an abnormal state, step d
Since the process moves from step 1 to step a, the sensor abnormality process shown in FIG. A gradual reduction process is then executed to gradually reduce the steering assist torque generated by the electric motor 7.

As described above, according to the second embodiment, the steering torque detection means includes the main and auxiliary steering torque sensors 9A and 9.
B, when an abnormality occurs in the main steering torque sensor 9A, the electric motor 7 can be controlled based on the steering torque detection value of the auxiliary steering torque sensor 9B, and the steering assist condition can continue,
Since the process of gradually decreasing the steering assist torque is executed only when both steering torque sensors become abnormal, a more reliable fail-safe function can be achieved. Moreover,
As in the above example, by setting the steering assist torque generated by the electric motor to be smaller than the normal state, the driver can be made to reliably recognize the abnormal state of the main steering torque sensor.

Note that in each of the above embodiments, the vehicle speed sensor 10
Although the vehicle speed sensitive type is described in which the steering assist torque generated by the electric motor 7 is changed in accordance with the detected vehicle speed value, the present invention is not limited to this. Further, in each of the above embodiments, a case has been described in which the control means is configured by the control device 8 to which the microcomputer 16 is applied, but instead of the microcomputer 16, it may be configured by combining electronic circuits such as a comparator and an arithmetic circuit. is also possible.

Furthermore, in the second embodiment, the case where two torque sensors, the main and auxiliary steering torque sensors 9A and 9B, are provided is described, but the present invention is not limited to this, and three or more torque sensors may be provided. It may also be provided.

[0050]

As described above, according to the invention of claim 1, when an abnormality occurs in the steering torque detection means, the abnormality detection means detects the abnormality, and the voltage gradual reduction means provided in the control means Since the drive voltage to the motor is gradually reduced, it is possible to gradually reduce the steering assist torque generated by the electric motor when an abnormality occurs in the steering torque detection means, thereby preventing kickback of the steered wheels. At the same time, by gradually increasing the steering feel of the steering wheel, the driver can directly recognize the occurrence of an abnormality, and can take appropriate actions such as stopping the vehicle in order to deal with the occurrence of an abnormality. This makes it possible to achieve the effect of achieving a smooth fail-safe function.

According to the second aspect of the invention, when an abnormality occurs in the steering torque detection means, the abnormality detection means detects the abnormality, and the input switching means provided in the control means changes the input steering torque. Since the configuration is such that the detected value is switched from the main steering torque sensor to the auxiliary steering torque sensor, even if an abnormality occurs in the main steering torque sensor, steering control can be performed based on the steering torque detection value of the auxiliary steering torque sensor. This can be continued, and the effect of achieving a more reliable fail-safe function can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a claim correspondence diagram corresponding to claim 1.

FIG. 2 is a claim correspondence diagram corresponding to claim 2.

FIG. 3 is a schematic configuration diagram of a first embodiment of the present invention.

FIG. 4 is a block diagram showing a control device of the first embodiment.

FIG. 5 is a flowchart showing steering control processing in the microcomputer of the first embodiment.

FIG. 6 is a flowchart showing sensor abnormality processing in the microcomputer of the first embodiment.

FIG. 7 is a characteristic diagram showing an example of a storage table showing the relationship between the steering assist torque value and the motor current setting value in the first embodiment.

FIG. 8 is a waveform diagram showing changes in the steering assist torque value with respect to time to explain the operation of the first embodiment.

FIG. 9 is an explanatory diagram showing a state in which the steering assist torque value gradually decreases with respect to time to explain the operation of the first embodiment.

FIG. 10 is a block diagram showing a control device according to a second embodiment of the present invention.

FIG. 11 is a flowchart showing steering control processing in the microcomputer of the second embodiment.

[Explanation of symbols]

1 Steering wheel 2 Steering shaft 3 Steering gear 7 Electric motor 8 Control device 9, 9A, 9B Steering torque sensor 11 Amplifier 16 Microcomputer 17 Motor drive circuit 20 Analog changeover switch

Claims (2)

[Claims] 1. Control for controlling a steering torque detection means for detecting a steering torque of a steering system, and an electric motor that generates a steering assist force for the steering system based on a steering torque detection value of the steering torque detection means. The electric power steering apparatus includes an abnormality detection means for detecting an abnormal state of the steering torque detection means and outputting an abnormality detection signal, and the control means detects an abnormality detection signal of the abnormality detection means. An electric power steering device comprising: a torque gradual reduction means for gradually reducing the steering assist torque generated by the electric motor when the electric motor receives a torque. 2. Control for controlling a steering torque detection means for detecting a steering torque of a steering system, and an electric motor that generates a steering assist force for the steering system based on a steering torque detection value of the steering torque detection means. The electric power steering apparatus includes an abnormality detection means for detecting an abnormal state of the steering torque detection means and outputting an abnormality detection signal, and the steering torque detection means includes at least a main steering torque detector and a main steering torque detector. The control means includes two torque detectors, an auxiliary steering torque detector, and when receiving an abnormality detection signal from the abnormality detection means, the control means transfers the input steering torque detection value from the main steering torque detector to the auxiliary torque detector. An electric power steering device comprising an input switching means for switching to a steering torque detector.