JP2004299616A - Fail safe controlling mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform fail safe control appropriate in response to an actual state by varying threshold value according to a condition, in a power steering device comprising a steering torque sensor 9 for detecting the steering torque, a vehicle speed sensor 10 for detecting a vehicle speed, and a control means C for controlling an assist means based on signals from the steering torque sensor 9 and vehicle speed sensor 10. <P>SOLUTION: The control means C comprises an output section 11 for identifying an assist signal to be outputted to the assist means and an abnormal detecting section 12 for determining abnormality. The abnormal detecting section 12 has a function of storing a table T for identifying risk based on the signals from the steering torque sensor 9 and vehicle speed sensor 10, setting the threshold value for determining the abnormality according to the risk, calculating difference between the assist signal identified by the output section 11 and a signal fed back to the control means C, and determining abnormality when the absolute value of the difference exceeds the threshold value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fail-safe control mechanism used for a power steering device, for example.
[0002]
[Prior art]
FIG. 5 is an overall configuration diagram of a conventional electric power steering device.
As shown in FIG. 5, an input shaft 2 is connected to the handle 1, and the input shaft 2 and the output shaft 3 are connected by a torsion bar 4. A pinion 5 is provided at the tip of the output shaft 3, and the pinion 5 is engaged with a rack 6. The rack 6 is formed on a rod 7, and wheels A, A are linked to both ends of the rod 7.
[0003]
Further, a pinion 8 fixed to the output shaft of the electric motor M is engaged with the rack 6. The electric motor M is controlled by a control unit c. The control unit c is connected with a steering torque sensor 9, a vehicle speed sensor 10, and a driving unit D.
The steering torque sensor 9 detects the steering torque from the amount of twist of the torsion bar 4, and the vehicle speed sensor 10 detects the speed of the vehicle. Further, the driving means D outputs a current corresponding to a signal output from the control means c to the driving motor M.
[0004]
When the steering wheel 1 is turned, the steering torque sensor 9 detects the steering torque generated at that time, and outputs a torque signal corresponding to the magnitude of the steering torque to the control means c. The vehicle speed sensor 10 detects the vehicle speed of the vehicle, and outputs a vehicle speed signal to the control means c.
The control means c specifies an assist signal from the input torque signal and vehicle speed signal, and outputs the signal to the driving means D.
The driving unit D that has received the assist signal from the control unit c outputs a current corresponding to the signal to the electric motor M. The electric motor M is driven according to the current to rotate the pinion 8. When the pinion 8 rotates, the rod 7 moves together with the rack 6, and the wheels A, A are steered.
[0005]
FIG. 6 is a block diagram of the circuit of the control means c.
The control unit c includes an output unit 11 and an abnormality detection unit 12. The output unit 11 specifies an assist signal from the torque signal and the vehicle speed signal, and outputs the signal to the driving unit D. .
The abnormality detection unit 12 calculates the difference between the assist signal output from the output unit 11 and the current value output from the driving unit D and fed back using the same physical quantity, and determines whether the difference is abnormal. Is what you do. In order to determine whether or not there is an abnormality, the abnormality detection unit 12 stores a preset threshold value, and determines that the abnormality is abnormal when the absolute value of the calculated difference exceeds the threshold value.
[0006]
When the abnormality detection unit 12 determines that an abnormality has occurred as described above, the abnormality detection unit 12 outputs an abnormality signal to the output unit 11. The output unit 11 that has received the abnormal signal outputs a predetermined signal to the driving unit D. The driving unit D that has received the signal stops energizing the electric motor M. When the energization is stopped, the electric motor M is not driven, and the mode is switched to manual steering.
By switching to manual steering as described above, a fail-safe state is established.
[0007]
[Patent Document 1]
JP-A-6-270823
[Problems to be solved by the invention]
The above-described conventional apparatus determines whether or not an abnormality is present on the basis of a threshold, but the threshold is fixedly set. As described above, when the threshold value is fixed, there is a problem that appropriate fail-safe control cannot always be performed in accordance with the driving situation.
For example, if the threshold value is set to a small value, even if the difference calculated by the abnormality detection unit 12 becomes slightly larger, the difference may exceed the set threshold value. It switches to the state. However, if the vehicle is stationary, even if the wheels are turned on their own, it is not so dangerous. In other words, although it is abnormal if the judgment is made based on the threshold value, it may not always be necessary to switch to the fail-safe state in consideration of the above-mentioned running conditions.
[0009]
Conversely, if the threshold value is set to a relatively large value, the threshold value may not exceed the set threshold value even if the difference calculated by the abnormality detection unit 12 increases. Does not switch. However, during high-speed running, the vehicle is largely bent by slightly turning the wheels, so that if the wheels are turned against the driver's intention due to the abnormal signal, a traveling problem may occur. In other words, it is not abnormal if the judgment is made based on the threshold value, but in consideration of the above-mentioned running conditions, there is a case where the user always wants to switch to the fail-safe state.
[0010]
For this reason, it is very important to set the threshold level to a certain level.However, considering various driving situations, it is difficult to set the threshold level, and it is difficult to set an appropriate level. Could not be set.
[0011]
As described above, in the conventional apparatus, since the threshold value is fixedly set, there is a problem that the above-described inconvenience occurs.
An object of the present invention is to provide a fail-safe control mechanism that can perform appropriate fail-safe control according to an actual situation by making a threshold value variable according to conditions.
[0012]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a power supply comprising: a steering torque sensor for detecting a steering torque; a vehicle speed sensor for detecting a vehicle speed; and control means for controlling an assist means based on signals from the steering torque sensor and the vehicle speed sensor. In the steering device, the control unit includes an output unit that specifies an assist signal to be output to the assist unit, and an abnormality detection unit that determines abnormality. The abnormality detection unit is configured to output signals from a steering torque sensor and a vehicle speed sensor. A table that specifies the degree of danger based on the danger is stored, and a threshold value for determining an abnormality is set according to the degree of danger. It is characterized in that it has a function of calculating the difference and determining that the difference is abnormal when the absolute value of the difference exceeds a threshold value.
[0013]
In the second invention, the abnormality detection unit stores a table that specifies a lower risk as the vehicle speed is lower and the steering torque is higher, and specifies a higher risk as the vehicle speed is higher and the steering torque is lower. It is characterized in that the lower the threshold, the larger the threshold is set, and the higher the risk, the smaller the threshold is set.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 4 show an embodiment of the present invention.
The basic structure of the electric power steering apparatus according to this embodiment is the same as that of the conventional technology, and therefore, the same components as those of the conventional technology are denoted by the same reference numerals.
FIG. 1 is an overall configuration diagram of the electric power steering device.
As shown in FIG. 1, an input shaft 2 is connected to the handle 1, and the input shaft 2 and the output shaft 3 are connected by a torsion bar 4. A pinion 5 is provided at the tip of the output shaft 3, and the pinion 5 is engaged with a rack 6. The rack 6 is formed on a rod 7, and wheels A, A are linked to both ends of the rod 7.
[0015]
Further, a pinion 8 fixed to the output shaft of the electric motor M is engaged with the rack 6. The electric motor M is controlled by a control means C. The control means C is connected to a steering torque sensor 9, a vehicle speed sensor 10, and a driving means D.
The steering torque sensor 9 detects the steering torque from the amount of twist of the torsion bar 4, and the vehicle speed sensor 10 detects the speed of the vehicle. The driving means D outputs a current corresponding to a signal output from the control means C to the driving motor M.
In this embodiment, the electric motor M and the driving means D constitute the present invention.
[0016]
When the steering wheel 1 is turned, the steering torque sensor 9 detects the steering torque generated at that time, and outputs a torque signal corresponding to the magnitude of the steering torque to the control means C. The vehicle speed sensor 10 detects the vehicle speed of the vehicle, and outputs a vehicle speed signal to the control means C.
The control means C specifies an assist signal from the input torque signal and vehicle speed signal, and outputs the signal to the driving means D.
The driving means D which has received the assist signal from the control means C outputs a current corresponding to the signal to the electric motor M. The electric motor M is driven according to the current to rotate the pinion 8. When the pinion 8 rotates, the rod 7 moves together with the rack 6, and the wheels A, A are steered.
[0017]
FIG. 2 is a block diagram of a circuit of the control means C.
The control unit C includes an output unit 11 and an abnormality detection unit 12. The output unit 11 specifies an assist signal from the torque signal and the vehicle speed signal, and outputs the signal to the driving unit D.
The abnormality detection unit 12 calculates a difference between the assist signal output from the output unit 11 and the current value output from the driving unit D and fed back, and determines whether the difference is abnormal. In order to determine whether or not there is an abnormality, the abnormality detection unit 12 stores a changeable threshold value, and determines that the threshold value is abnormal when the absolute value of the calculated difference exceeds the threshold value.
[0018]
Further, the abnormality detection unit 12 stores a table T shown in FIG.
The table T includes a torque signal column 13, a vehicle speed signal column 14, and a risk level column 15, as shown in FIG.
The torque signal column 13 divides the torque signal into three levels of “small”, “medium”, and “large” according to the magnitude of the steering torque.
The vehicle speed signal column 14 divides the vehicle speed signal into four stages of "0", "low speed", "medium speed", and "high speed" according to the vehicle speed. In this embodiment, “0” indicates 0 km / h, and “low speed” indicates a speed of 1 to 20 km / h. Further, "medium speed" indicates 21 to 50 km / h, and "high speed" indicates a speed of 51 km / h or more. The above speed can be arbitrarily changed.
[0019]
The risk level column 15 specifies the risk level based on the torque signal and the vehicle speed signal.
In this embodiment, the risk is divided into three levels of “low”, “medium”, and “high”, and the risk is specified as follows.
When the vehicle speed signal is “0”, the degree of danger is “low” regardless of the magnitude of the torque signal. This is because if the vehicle speed is 0 km / h, the risk is considered to be low because the vehicle is stopped even if the wheels are turned without permission.
[0020]
When the vehicle speed signal is “low speed”, that is, when the speed is 1 to 20 km / h, when the torque signal is “small”, the danger level is “medium”. This is because when the torque signal is “small”, it is considered that there is a risk that the wheels are turned without permission against the driver's will. That is, the case where the torque signal is “small” means that the steering torque of the driver is small, and the electric motor M exerts an abnormal assist force based on the abnormal signal output from the driving unit D. The assist force often exceeds the driver's steering torque. When the abnormal assist force exceeds the steering torque of the driver, the wheels are turned without permission, which is considered to be dangerous. For this reason, when the torque signal is “small”, the risk level is set to “medium”.
[0021]
When the torque signal is “medium” and “large”, the risk level is “low”. This is because, when the torque signal is “medium” or “large”, it is considered that the turning of the wheel by itself can be suppressed by the strength of the driver. That is, the case where the torque signal is “medium” or “large” means that the electric motor M exerts an abnormal assist force based on the abnormal signal output from the driving means D because the steering torque of the driver is large. However, the steering torque of the driver often exceeds the assist force. When the steering torque of the driver exceeds the abnormal assist force, it is considered that the wheels can be prevented from turning without permission. For this reason, when the torque signal is “medium” or “large”, the risk level is set to “low”.
[0022]
When the vehicle speed signal is “medium speed”, that is, when the speed is 21 to 50 km / h, when the torque signal is “small”, the danger level is set to “high”. This is because it is considered that there is a higher danger when the wheels are turned on their own accord against the driver's will during low-speed running than during low-speed running.
When the torque signal is “medium”, the risk level is “medium”. This is because, similarly to the case where the torque signal is “small”, it is considered that there is a higher risk when the wheels are turned without permission during the middle speed running than during the low speed running.
Further, when the torque signal is “large”, the degree of danger is set to “low”. This is because, when the torque signal is “large”, it is considered that the turning of the wheels can be suppressed by the driver's arm strength, as in the case where the vehicle speed signal is “low”.
[0023]
When the vehicle speed signal is “high speed”, that is, when the speed is 51 km / h or more, when the torque signal is “small” and “medium”, the risk level is “high”. This is because, during high-speed running, even if the wheels are slightly steered, the vehicle is greatly bent, and thus it is considered that the risk is higher than during medium-speed running.
When the torque signal is “large”, the risk level is “medium”. During high-speed driving, as with the torque signal "small" and "medium", the vehicle turns greatly even if the wheels are slightly steered, so it is considered that the risk is higher than during medium-speed driving. Because it can be done.
[0024]
The abnormality detection unit 12 sets a threshold value according to the degree of risk specified as described above. That is, when the risk is “medium”, the threshold is set based on a certain criterion. When the risk is “low”, the threshold is set to be larger than when the risk is “medium”. If the threshold value is set to a relatively large value, the state is not switched to the fail-safe state even if the absolute value of the difference calculated by the abnormality detection unit 12 is slightly larger. Then, when the risk is “high”, the threshold value is set smaller than when the risk is “medium”. If the threshold value is set to a small value, the state is switched to the fail-safe state even if the absolute value of the calculated difference is small.
[0025]
Next, a detection procedure of the abnormality detection unit 12 will be described based on a flowchart shown in FIG.
When the torque signal and the vehicle speed signal are input in step 1, the abnormality detection unit 12 sets the degree of risk from the table T based on the torque signal and the vehicle speed signal input in step 2. After setting the risk, a threshold is set in step 3 according to the risk.
On the other hand, in step 4, the assist signal output from the output unit 11 and the current value output from the driving unit and fed back are input. When the assist signal and the fed back current value are input, the difference between the input assist signal and the fed back current value is calculated by the same physical quantity in step 5, and the process proceeds to step 6.
[0026]
In step 6, the threshold value set in step 3 is compared with the absolute value of the calculated difference.
As a result of the comparison, if the absolute value of the difference exceeds the threshold value, it is determined that an abnormality has occurred, and an abnormality signal is output to the output unit 11 in step 7.
Conversely, when the absolute value of the difference is equal to or smaller than the threshold value, it is determined that the operation is normal, and normal control is performed by the assist signal specified by the output unit 11 in step S8.
When the calculated difference is determined to be abnormal in step 7, the abnormality detection unit 12 outputs an abnormality signal to the output unit 11. The output unit 11 that has received the abnormal signal outputs a predetermined signal to the driving unit D. The driving unit D that has received the signal stops energizing the electric motor M. When the energization is stopped, the electric motor M is not driven, and the mode is switched to manual steering.
[0027]
By switching to manual steering as described above, it is possible to realize a highly reliable electric power steering device that does not enter a fail-safe state and does not perform steering contrary to the driver's will.
In this embodiment, the drive unit D feeds back the current value output to the electric motor M. However, for example, the output unit 11 may feed back the signal output to the drive unit D. That is, any signal may be fed back as long as the signal is output from the output unit 11 of the control unit C.
[0028]
According to the above-described embodiment, the abnormality detection unit 12 sets the risk from the table T based on the input torque signal and the vehicle speed signal, and sets the threshold value according to the risk. Therefore, it is easy to prevent switching to the fail-safe state when it is not necessary to switch to the fail-safe state, and to prevent switching to the fail-safe state when the switching is desired. That is, it is possible to perform appropriate fail-safe control according to the actual driving situation.
[0029]
Note that the table T and the threshold value in the above embodiment are merely examples, and may have a tendency as described below.
The risk is specified to be lower as the vehicle speed is lower and the steering torque is higher, and the threshold value is set higher according to the risk. Conversely, the higher the vehicle speed and the smaller the steering torque, the higher the risk is specified, and the threshold value is set smaller according to the risk. That is, it is only necessary that the above tendency is attained, and the specific value does not matter.
[0030]
Further, in the above-described embodiment, the risk level of the table T is divided into three levels of “low”, “medium”, and “high”. If the risk is subdivided, the threshold can be set more finely. Therefore, it is possible to further perform appropriate fail-safe control according to the driving situation.
Further, in the above embodiment, when the abnormality detection unit 12 determines that an abnormality has occurred, the state is switched to the fail-safe state. However, the driver may be notified that the abnormality has been determined. For example, at the same time as switching to the fail-safe state, an alarm may sound or a warning lamp may blink.
[0031]
Furthermore, the electric power steering device of the above embodiment is a two-pinion type in which the input shaft 2 side and the output shaft of the electric motor M are engaged with the rack 6, respectively. However, another type of electric power steering device may be used. For example, the fail-safe control mechanism of the present invention may be applied to a one-pinion type electric power steering device in which the output shaft 3 on the input shaft 2 side is directly rotated by the electric motor M.
Furthermore, the fail-safe control mechanism of the present invention is not limited to the power steering apparatus as in the above-described embodiment, but detects a failure of a device that needs to be changed to a fail-safe state by changing a threshold value according to conditions. It can be adopted for all mechanisms.
[0032]
【The invention's effect】
According to the first and second aspects of the present invention, since the threshold value is made variable in accordance with the condition, appropriate fail-safe control can be performed in accordance with the actual situation.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a block diagram of a control device.
FIG. 3 is a diagram showing a table stored in an abnormality detection unit.
FIG. 4 is a flowchart illustrating a detection procedure of an abnormality detection unit.
FIG. 5 is an overall configuration diagram of a conventional electric power steering device.
FIG. 6 is a block diagram of a conventional control device.
[Explanation of symbols]
9 Steering torque sensor 10 Vehicle speed sensor 11 Output unit 12 Abnormality detection unit C Control means M Drive motor T Table

Claims (2)

A power steering apparatus comprising: a steering torque sensor for detecting a steering torque; a vehicle speed sensor for detecting a vehicle speed; and control means for controlling assist means based on signals from the steering torque sensor and the vehicle speed sensor. The means includes an output unit that specifies an assist signal to be output to the assist unit, and an abnormality detection unit that determines abnormality. The abnormality detection unit specifies a degree of risk based on signals from a steering torque sensor and a vehicle speed sensor. And a threshold for judging an abnormality according to the degree of risk is set, and a difference between the assist signal specified by the output unit and a signal fed back to the control means is calculated. A fail-safe control mechanism having a function of determining an abnormality when the absolute value of the difference exceeds a threshold value. The abnormality detection unit specifies a lower risk level as the vehicle speed is lower and the steering torque is higher, and stores a table that specifies a higher risk level as the vehicle speed is higher and the steering torque is lower. 2. The fail-safe control mechanism according to claim 1, wherein the threshold value is set to be large, and the threshold value is set to be small as the degree of risk is high.

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