Vehicle steering apparatus

A vehicle steering apparatus with improved safety securely detects whether or not a backup system is operable and comprises a steering shaft connected to the steering wheel; a reaction actuator connected to the steering shaft for adding a reaction force; a rack for steering a steered wheel; a steering actuator provided on the rack; a backup mechanism for connecting the steering shaft and the rack via a clutch, a first detection means or mechanism for detecting the condition of the steering shaft, a second detection means or mechanism for detecting the condition of the rack, and a backup operation monitoring means or mechanism for driving the steering actuator when the power source is energized, the backup operation monitoring means or mechanism selectively monitoring the operation of the backup mechanism based on the value detected by the first detection means or mechanism or the second detection means or mechanism or both.

RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2004-380951, filed Dec. 28, 2004, including its specification, claims and drawings, is incorporated herein by reference in its entirety.

FIELD

Described herein is a vehicle steering apparatus, and more particularly, a steering apparatus operated by steer-by-wire control and having a backup system.

BACKGROUND

Conventional vehicle steering technology of the type employs so-called steer-by-wire control, and the steering wheel and the steered wheels are connected by a clutch. In the normal condition, however, the steering wheel and the steered wheels are mechanically separated by releasing the clutch, and steering is carried out by driving an actuator connected to the steered wheels by detecting the steering manually exercised by the driver. A backup system is provided to engage the clutch and secure manual steering by mechanically connecting the steering wheel and the steered wheels.

However, in the prior art, the backup system operates only during a failed condition, and therefore steer-by-wire control may be initiated even when the backup system is in an abnormal condition. Consequently, the backup system cannot be guaranteed to operate in the failed condition.

SUMMARY OF THE INVENTION

The present steering apparatus takes into account the above-described problem, and provides improved safety by securely detecting whether or not the backup system is operable.

The present vehicle steering apparatus comprises a steering shaft connected to the steering wheel; a reaction actuator connected to the steering shaft for adding a reaction force; a rack for steering a vehicle wheel; a steering actuator provided on the rack; and a backup mechanism connecting the steering shaft and the rack via a clutch. A first detection means or mechanism is provided for detecting the condition of the steering shaft, and a second detection means or mechanism is provided for detecting the condition of the rack. The clutch is in an engaged condition when the power source of the steering apparatus is deenergized. A backup operation monitoring means or mechanism is provided for driving the steered actuator when the power source is energized and for monitoring the operation of the backup mechanism based on the detected value by the first detection means or mechanism and/or the second detection means or mechanism.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1is a schematic view of the present vehicle steering apparatus having a steering side at the right-hand portion of the figure near a steering wheel1, and a steered side at the left-hand portion of the figure near a steered wheel20of the vehicle. The apparatus includes the steering wheel1and a steering shaft2rotatably supported on the vehicle body and connected to the steering wheel1. On the steering shaft2is a steering angle sensor8that detects steering angle as the degree of steering by the driver, and a torque sensor9that detects steering torque as the degree of steering by the driver.

On the steering side is a reaction motor3that adds steering reaction to steering input generated by the driver's operation of steering wheel1. A steering side resolver10is provided in the steering motor3for detecting the rotation angle of the reaction motor3. Also on the steering side is an electromagnetic clutch6for physically engaging and releasing a connection between the steering shaft2and a backup mechanism7.

The backup mechanism7comprises a steering side cable pulley7ahaving one end thereof connected to the electromagnetic clutch6; a steered side cable pulley7bhaving one end thereof connected to a pinion shaft15; and two cables7cand7dthat connect both cable pulleys7aand7bin a condition in which they are coiled in opposite directions from each other. When the electromagnetic clutch6is released, the rotation of the steering shaft2is not transmitted to the pinion shaft15.

When the steering wheel1is rotated in one direction while the electromagnetic clutch6is engaged, one of the two cables7cand7dtransmits the steering torque input from the driver, and the other cable transmits the reaction torque input from the steered vehicle wheel20, thereby performing a function equivalent to that of the steering shaft2.

For steering the steered wheel20, the pinion shaft15is rotatably supported on the vehicle body and one end thereof is connected to the steered wheel cable pulley7b. A steered motor5, a steered side resolver11, a steered side torque sensor12, and a rotary encoder13are provided on the pinion shaft15.

The steered motor5provides steered torque to the pinion shaft15, and the steered side resolver11detects the rotation angle of the steered motor5. The steered side torque sensor12is provided between the steered motor5and steered vehicle wheel20for detecting the rotational torque of the pinion shaft15. The rotary encoder is provided to detect the rotational angle of the pinion shaft15.

On the steered wheel side of the pinion shaft15, a rack and pinion mechanism (not shown) is provided for effecting the steering of the steered wheel20by moving the steering rack4in the axial direction.

A lock mechanism30that limits rotation of the steering wheel1is provided on the steering shaft2to prevent the steering wheel1from rotating during initial monitoring.

FIG. 2is a block diagram showing the structure of the control unit14. The control unit14comprises a steer-by-wire controller141, a clutch controller142, an error detector143, and a fail-safe processor144.

The steering angle, steering torque and reaction motor rotation angle are inputs from the steering angle sensor8, steering side torque sensor9and steering side resolver10, respectively. In addition, the steered motor rotation angle, steered torque, and pinion shaft rotation angle are inputs from the steered side resolver11, steered side torque sensor12and rotary encoder13, respectively, as well as there being sensor signals, etc., that are inputs from other sensors (vehicle speed sensor, yaw rate sensor, lateral acceleration sensor, etc.)

The steer-by-wire controller141generates a control signal so that the steering reaction torque corresponding to the driving condition is added to the reaction motor3. The steer-by-wire controller also generates a control signal so that the amount of steering corresponding to the driving conditions and the steering condition imposed by the driver are added to the steered motor5.

The clutch controller142effects engagement and release of the electromagnetic clutch6. It releases the electromagnetic clutch6while executing the normal steer-by-wire control and it engages the electromagnetic clutch6when the ignition is turned off (when the power is off) or during fail-safe control.

The error detector143effects the initial monitoring control that determines whether or not the backup mechanism7is working normally. In the first embodiment, both the reaction motor3and steered motor5are driven at the same torque T in such a direction that each other's torque is offset, and the detected values T1and T2of the steering side torque sensor9and12are compared. If the error between T1and T2is within the predetermined range, it determines that the torque transmission of the steering side and steered side are being carried out via backup mechanism7without any abnormality, and the normal steer-by-wire control is executed.

The fail-safe controller144carries out the fail-safe control when the error detector143determines that the error is outside the predetermined range. In the first embodiment, after the warning lamp21is lit, an appropriate operation is performed, such as preventing the vehicle from starting or setting off an alarm device.

In order to determine whether the backup mechanism7is operating without any abnormality, the error detector143effects the initial monitoring control. In order to secure manual steering in the case of failure while parking, the electromagnetic clutch6is in an engaged condition when the ignition is turned off. In the first embodiment, an arbitrary torque T is first generated at the reaction motor3, and the same torque value T is transmitted to the counter steered motor5. At this time, torque T is such that the steered wheel20does not effect steering; more specifically, it is a smaller torque than the road surface reaction torque of the steered wheel20. In this way, the steered wheel20will not be turned by the initial monitoring control and therefore causes no anxiety for the driver.

At this time, the detected values T1and T2of the steering side and steered side torque sensors9and12are compared and if the error between T1and T2is within the predetermined range, it is determined that the torque transmission of the steering side and steered side is being carried out via the backup mechanism7without any abnormality, and the normal steer-by-wire control is executed.

When the error between detected T1and T2is outside the predetermined range, it determines that there is abnormality in the torque transmission via the backup mechanism7, and manual steering has failed, so that a fail-safe operation is performed, such as preventing the vehicle from starting or the setting off of an alarm device.

FIG. 3is a flowchart showing the initial monitoring control process according to the first embodiment. Each step is described as follows.

At step S101, it is determined whether or not the ignition is turned on. If it is YES, the process advances to step S102and if it is no, the control is terminated.

At step S102, it is determined whether or not the steer-by-wire control permission flag is established. If it is YES, the process advances to step S112, and if it is NO, it advances to step S103.

At step S103, the electromagnetic clutch6is energized and the process advances to step S104.

At step S104, the reaction motor3and steered motor5are turned on, torque T is generated for each of them and then the process advances to step S105.

At step S105, it is determined whether the relative error of the detected values T1and T2of the steering side and steered side torque sensors9and12is within the predetermined value εT. If it is YES, the process advances to step S106, and if it is NO, it advances to step S109. This predetermined value εTis configured by taking into account the offset value of the torque, the friction of the backup mechanism7, etc.

At step S106, the reaction motor3and the steered motor5are turned off and the process advances to step S107.

At step S107, the electromagnetic clutch6is released and the process advances to step S108.

At step S108, the steer-by-wire control permission flag is established and the control is completed.

At step S109, the reaction motor3and the steered motor5are turned off and the process advances to step S110.

At step S110, the warning lamp is turned on and the process advances to step S111.

At step S111, the fail-safe processing is carried out and the control is completed. With the fail-safe processing, the driver's attention can be attracted by an alarm, etc., or safety can be ensured by not starting the engine even if the ignition is turned on.

At step S112, the steer-by-wire control is executed and the control is completed.

In the first embodiment, in order to determine whether the backup mechanism7is operating without any abnormality, the same torque value T is applied to the reaction motor3and the steered motor5, and the detected values T1and T2of the steering side torque sensor9and the steered side torque sensor12are compared. If the error between T1and T2is within the predetermined range, it is determined that the torque transmission of the steering side and steered side can be carried out via the backup mechanism7without abnormality, and normal steer-by-wire control is executed. If the error is outside the predetermined range; more specifically, the torque transmission via the backup mechanism7is not carried out and the sum of the absolute value of the detected values T1and T2is 2T, then it is determined that the torque transmission via the backup mechanism7is not being carried out normally, and manual steering cannot be secured, and thus, the fail-safe process is carried out.

This allows detection of whether the backup mechanism7will operate securely, and consequently, a vehicle steering apparatus with improved safety can be provided. In addition, the steering wheel1is secured by the lock mechanism30and therefore the steering wheel will not rotate a large amount due to the initial monitoring, thereby alleviating driver anxiety.

The second embodiment is described with reference toFIG. 4. The basic structure is the same as in the first embodiment and therefore only the differences are described. The first embodiment is provided with a lock mechanism30and it is determined whether the relative error of detected values T1and T2of the steering side and steered side torque sensor9and12is within the predetermined value εT. The second embodiment is different from the first embodiment in that the lock mechanism is not provided and initial monitoring is carried out based on the detected value T2provided by the steered side torque sensor12.

The control unit14according to the second embodiment is the same as that of the first embodiment except for the error detector143. The error detector143according to the second embodiment is driven by the same torque amount T in the direction in which the torque of the reaction motor3and steered motor5offset each other. In other words, if the torque direction of the reaction motor3is positive, the reaction motor3generates torque T and the steered motor5generates torque −T.

At that time, the torque T2that affects the rack4is detected by the steered side torque sensor12. When there is no abnormality in the backup mechanism7, the reaction motor3and the steered motor5generate the same torque and restrain each other's rotation. Therefore the rack4hardly rotates. Consequently, if the detected value T2from the steered side torque sensor12is within the predetermined range, the backup mechanism7is determined to be normal. If T2exceeds the predetermined range, it is determined that the torque of the steered motor5is not being transmitted to the steering shaft side and the backup mechanism7is determined to be in an abnormal condition.

In addition, by taking advantage of the fact that when there is no abnormality in the backup mechanism7, the reaction motor3hardly rotates, and that it rotates during the abnormal condition, the abnormality can be detected when the detected value Ns of the steering angle sensor8is a predetermined value or greater. When rotation of the steering wheel1is detected, the torque T provided to each motor should be larger than the inertia of the steering wheel1, so that rotation can be securely detected. The generation of the rotation angle is set within the range of ±10° as the steering angle, so that rotation can be securely detected without any anxiety for the driver.

In order to determine whether the backup mechanism7can operate without any abnormality, the error detector143carries out the initial monitoring control. In order to secure manual steering in case there is a failure while the vehicle is being parked, the electromagnetic clutch6is engaged when the ignition is turned off. In the second embodiment, an arbitrary torque T is generated at the reaction motor3and the same torque value T is generated at the steered motor5.

If there is no abnormality in the backup mechanism7, the transmission of the mobile power between the steering wheel1and rack4is carried out without abnormality and the reaction motor3and steered motor5generate the same torque and so constrain each other's rotation; therefore the steering shaft2and the rack hardly rotate (only when each other's motor rotation error is εs). Thus, if εt is the predetermined error and the detected value T2of the steered side torque sensor12is within the range of −εt≦T2≦εt, and the detected value Ns of the steering angle sensor8is within the rotation error εs of each of motors3and5, then backup mechanism7is determined to be normal and the normal steer-by-wire control is executed.

When there is abnormality in the backup mechanism7and the mobile power is not transmitted from the steering wheel1to the rack4, then all of the torque of the steered motor5is transmitted to the rack4. This affects the steered torque sensor12and the detected value of torque T2will exceed the error εt. In addition, the detected value Ns of the steering angle sensor8increases by exceeding the rotation error εs of each of the motors3and5.

In addition, in the normal condition the reaction motor3hardly rotates, and therefore the electric current value has a step waveform in which it starts at the same time as system startup. On the other hand, in an abnormal condition, the rotation of the reaction motor3is not restricted and therefore it has a delayed waveform in which the electric current value gradually increases (SeeFIG. 5). Here the steer-by-wire control is so structured that a target angle advanced from the current angle by the amount of the predetermined angle in the direction that the reaction is applied, as the control of the reaction motor and an electric current command value are calculated based on the deviation of the target angle and the current actual angle. In other words, because when the motor does not rotate the deviation is not eliminated, the electric current value rises at once. When the motor rotates, the deviation is appropriately eliminated and the electric current value gradually increases. When the motor is controlled by the torque control, etc., the torque can be estimated by detecting the transition of the electric current value for the portion of the back electromotive force along with the motor rotation.

Therefore, when the detected value T2of the steered side torque sensor12exceeds the predetermined error ±εt or the detected value Ns of the steering angle sensor8exceeds the rotation error εs of each of the motors3and5, then abnormality of the backup mechanism7is detected and fail-safe processing is carried out. In addition to the determination of T2, by detecting the delayed response of the electric value of the reaction motor3, the reliability of the abnormality determination is improved.

FIG. 4is a flowchart showing the initial monitoring control process in accordance with the second embodiment. Each step is described as follows.

Steps S201to S204are the same as steps S101to S104according to the first embodiment.

At step S105, it is determined whether the detected value T2of the steered side torque sensor12exceeds the threshold value εt, or whether the rotation angle Ns of the steering shaft2exceeds the threshold value εs. If it is YES, the process advances to step S206, and if it is NO, the process advances to step S209.

Steps S206to S212are the same as steps S106to S112according to the first embodiment.

In the second embodiment, the torque T2that affects the rack3detects the normal/abnormal operation of the backup mechanism7by means of the steered side torque sensor12. If the detected value T2of the steered side torque sensor is within the range of −εt≦T2≦εt, then the backup mechanism7is determined to be normal, and the normal steer-by-wire control is executed. If the detected value T2of the steered torque sensor12exceeds the predetermined error ±εt or if the detected value Ns of the steering angle sensor8exceeds the rotation error εs for both motors3and5, then the abnormality in the backup mechanism7is detected and the fail-safe process is carried out.

By doing so, the initial monitoring can be carried out without a lock mechanism. In the normal condition, an initial monitoring is allowed without moving the steering wheel1, thereby not giving rise to anxiety in the driver. In principle, the initial monitoring can be carried out based on the detected value of the steered side torque sensor12only, and therefore a simple structure can be achieved, as compared to the first embodiment, which detects the torques of both the steering side and steered side. In addition, by detecting the delayed response of the electric

In the second embodiment, the detected value T2of the steered side torque sensor12was used for the determination; nonetheless, the rotation angle can be used for the determination. More specifically, when the speed reduction ratio of the steering side and steered side is r, if the steered motor5rotates through the rotation angle θ2, then the reaction motor3rotates θ2/r. Therefore, it is acceptable that the actual rotation angles θ1and θ2of the steering side and steered side are detected by the steering side and steered side resolvers10and11, and the actual rotation angle θ1of the reaction motor3and the rotation angle θ2/r; that is, the rotation of the steered side motor5, are compared, and if the error is within the predetermined value, the backup mechanism7is determined to be normal.

Or the steered side motor5is rotated by θ1×r due to the actual rotation angle θ1of the reaction motor3. Therefore it is acceptable that the actual rotation angle θ2of the steered side motor5and the rotation angle θ1×r; that is, the rotation of the reaction motor3, are compared and the error is calculated.

In the second embodiment, because the steering shaft2is not provided with a lock mechanism, the steering wheel1rotates along with the rotation of the reaction motor3, and the detection value at the steering side torque sensor9is 0 (in reality, torque used for the inertia of the steering wheel1is generated). Therefore, it is acceptable to carry out the initial monitoring control process by detecting the load torque T1of the reaction motor3based on the electric current value of the reaction motor3.

The third embodiment is described with reference toFIG. 6. The basic structure is the same as in the first embodiment and therefore only the differences are described. It is different in that, during the initial monitoring control according to the first embodiment, both the reaction motor and steered motor5are driven, while in the third embodiment, only the reaction motor3is driven. By detecting the torque T of the reaction motor3and making a comparison between the steering side and steered side torque sensors9and12, the initial monitoring of the backup mechanism7is carried out.

When there is no abnormality in backup mechanism7and manual steering is secured, the torque of the reaction motor3is transmitted to each member on the steered side via the backup mechanism7. Therefore in the third embodiment, when only the reaction motor3(or steered motor5) is driven, the torque generated between the reaction motor3and the lock mechanism30can be detected. Consequently, when the detected values of the steering side and steered side torque sensors9and12are determined to be approximately the same, the backup mechanism7is determined to be normal.

More specifically, when only the reaction motor3is driven and the torque T2detected by the steered side torque sensor12is the predetermined value or greater (the contortion of the reaction motor torque T is detected by two sensors, which are for the steering side and steered side, and the torque detected by the steered side torque sensor12is approximately T/2) then the error detector143determines that the torque transmission of the steering side and steered side can be effected via the backup mechanism7without abnormality, and the normal steer-by-wire control is performed. If T2is less than the predetermined value, it is determined that the torque transmission via the backup mechanism7cannot be carried out normally, and therefore a fail-safe operation is performed, such as preventing the vehicle from starting or setting off an alarm device.

FIG. 6is a flowchart showing the initial monitoring control process in accordance with the third embodiment. Steps S301to S303are the same as steps S101to S103in the first embodiment.

At step S304, only the reaction motor3is turned on and the process advances to step S305.

At step S305, it is determined whether the error of the torques T1and T2detected by the steering side and steered side torque sensors9and12is the predetermined value εTor less. If it is YES, the process advances to step S306, and if it is NO, the process advances to step S309.

At step S306the reaction motor3is turned off and the process advances to step S307.

Steps S307and S308are the same as steps S107and108ofFIG. 3.

At step S309, the reaction motor3is turned off and the process advances to step S310.

In the third embodiment, only the reaction motor3is operated and if the error of the torques T1and T2detected by the steering side and steered side torque sensors9and12is less than or equal to the predetermined value εT, then it is determined that the torque transmission between the steering side and steered side via the backup mechanism7is being carried out without abnormality, and the normal steer-by-wire control is executed. If the error is greater than the predetermined value εT, it is determined that the torque value of the steering torque sensor9is output and the torque value of the steered torque sensor12is not output and therefore the torque transmission via the backup mechanism cannot be carried out normally. Therefore a fail-safe operation is performed, such as preventing the vehicle from starting or setting off an alarm device.

By doing so, compared to the first embodiment, in which the initial monitoring is carried out by operating both the reaction motor3and the steered motor5, the initial monitoring of the backup mechanism7can be done with a simpler control.

The fourth embodiment is described with reference toFIG. 7. The basic structure is the same as in the second embodiment and the initial monitoring is carried out by the detected value T2of the steered side torque sensor12without a lock mechanism. In the second embodiment, both the reaction motor3and the steered motor5are operated; but the fourth embodiment differs from the second embodiment in that only the reaction motor3is operated.

The control unit14in the fourth embodiment is the same as that in the first and second embodiments except for the error detector143. The error detector143in the fourth embodiment operates only the reaction motor3, and the torque T2that affects the rack4is detected by the steered side torque sensor12. As in the second embodiment, if the detected value T2of the steered side torque sensor12is greater than the predetermined value, the backup mechanism7is determined to be normal. If it is equal to or less than the predetermined value (for example, 0), it is determined to be abnormal.

As in the second embodiment, it is acceptable to take advantage of the fact that if there is no abnormality in the backup mechanism7, the reaction motor3hardly rotates, and because it rotates during the abnormal condition, the abnormality can be detected when the detected value Ns of the steering angle sensor8becomes greater than the predetermined value.

When the backup mechanism has no abnormality, the mobile power is normally transmitted between the steering wheel1and the rack4, and the torque of the reaction motor3is transmitted from the rack4to the steered wheel20. Therefore, the rotation of the reaction motor is constrained. In order to avoid steering the steered wheel20during the initial monitoring, the generated torque at the reaction motor3should have a magnitude that will not steer the steered wheel20.

The reaction motor3adds torque to the rack4while its rotation is restricted, and therefore contortion generated at the steered side torque sensor12and the detected value Ns of the steering angle sensor8is hardly changed. (The change in Ns is only the portion from the contorted angle εs of the steered side torque sensor12). Consequently, if the detected value T2of the steered side torque sensor12is positive, the backup mechanism7is determined to be normal and the normal steer-by-wire control is executed.

If abnormality occurs in the backup mechanism7and the mobile power is not transmitted from the steering wheel1to the rack4, all the torque of the reaction motor3is transmitted to the steering shaft, and the steered side torque sensor12is not affected. Therefore torque T2becomes zero and the detected value Ns of the steering angle sensor8increases by exceeding the contortion angle εs of the steered side torque sensor12. In addition, as in the second embodiment, in the normal condition the reaction motor3hardly rotates and therefore the electric current value has a step waveform, in which it starts up at the same time as the system starts. On the other hand, in the abnormal condition, the rotation of the reaction motor3is not constricted and therefore it has a delayed waveform in which the electric current value gradually increases (SeeFIG. 5).

Therefore, if the detected value T2of the steered side torque sensor12is 0 or the detected value Ns of the steering angle sensor8exceeds the contortion angle s of the steered side torque sensor12, then abnormality in the backup mechanism7is detected and the fail-safe process is carried out. In addition, by detecting the delayed response of the electric current value of the reaction motor3in addition to the determination of T2and Ns, the reliability of the abnormality determination can be improved.

FIG. 7is a flow chart showing the initial monitoring control process according to the fourth embodiment. Each step is described as follows.

Steps S401to S404are the same as steps S101to S104in the first embodiment.

At step S405, it is determined whether the detected value T2of the steered side torque sensor12is 0 or the rotation angle Ns of the steering shaft2exceeds the threshold value εs. If it is YES, the process advances to step S406and if it is NO, the process advances to step S409.

Steps S406to S412are the same as steps S106to S112in the first embodiment.

The error detector143according to the fourth embodiment operates only the reaction motor3, and if the detected value T2of the steered torque sensor12is positive, the backup mechanism7is determined to be normal and the normal steer-by-wire control is executed. If the detected value T2of the steered torque sensor12is zero or the detected value Ns of the steering angle sensor8exceeds the contortion angle εs of the steered side torque sensor12, abnormality in the backup mechanism7is detected and the fail-safe process is carried out.

By doing so, the initial monitoring is carried out only with the reaction motor3operation, and consequently the effect of the second embodiment can be achieved with a simpler structure.

The fifth embodiment is described with reference toFIG. 8. The basic structure is such that, as in the third embodiment, a lock mechanism30is provided and the steering side and steered side torques are compared. However, while only the reaction motor3is operated in the third embodiment, in the fifth embodiment the initial monitoring is carried out by operating only the steered motor5.

FIG. 8is a flow chart showing the initial monitoring control process in the fifth embodiment.

Steps S501to503are the same as steps S101to S103in the first embodiment.

At step S504, only the steered motor5is turned on and the process advances to step S505.

At step S505, it is determined whether the error of the torques T1and T2detected by the steering side and steered side torque sensors9and12is the predetermined value εTor less. If it is YES, the process advances to step S506and if it is NO, the process advances to step S509.

At step S506, the steered motor5is turned off and the process advances to step S507.

Steps S507and S508are the same as steps S107and108ofFIG. 3.

At step S509, the steered motor5is turned off, and the process advances to step S510.

In the fifth embodiment, only the steered motor3is operated and if the error of the torques T1and T2detected by the steering side and steered side torque sensors9and12is within the predetermined range (for the steered motor torque T, the contortion is detected using two torque sensors at the steering side and steered side, and the torque detected by each of the torque sensors9and12becomes approximately T/2) then it is determined that the torque is being normally transmitted between the steering side and steered side via the backup mechanism7, and the normal steer-by-wire control is executed. If it is outside the predetermined range, it is determined that the torque transmission via the backup mechanism7is cannot be carried out normally, and the fail-safe process is carried out as in the other embodiments.

By doing so, as in the third embodiment, compared to the first embodiment that carries out the initial monitoring by operating both the reaction motor3and steered motor5, the initial monitoring of the backup mechanism7can be carried out with a simpler control. By employing the third or fifth embodiment, depending on the automobile design, the initial monitoring of the backup mechanism7can be easily carried out by operating either the steering side or steered side motors3or5.

The sixth embodiment is described with reference toFIG. 9. The basic structure is the same as in the second embodiment and therefore only the differences are described. In the second embodiment, both the reaction motor3and steered motor5are operated. The sixth embodiment differs from the second embodiment in that only the steered motor5is operated, and by detecting and comparing the rotation angles θ1and θ2of the reaction motor3and steered motor5, the initial monitoring is carried out.

If there is no abnormality in the backup mechanism7, when the steered motor5is rotated while the electromagnetic clutch6is engaged, the rotation is transmitted to the reaction motor3via the backup mechanism7. At this time, if the speed reduction ratio of the steering side and steered side is r, then the rotation angle of the reaction motor3relative to the rotation angle θ2of the steered motor5is θ2/r.

Therefore, in the sixth embodiment, the steered motor5is operated and it is determined whether the angle θ2/r of the reaction motor3via the backup mechanism7is rotated to the predetermined value Nθ2or greater.

If the angle θ2/r is the predetermined value Nθ2or greater, it is determined that the torque transmission between the steering side and steered side via the backup mechanism7is being carried out normally, and the normal steer-by-wire control is executed. If it is less than the predetermined value Nθ2, then the fail-safe process is carried out such as in the other embodiments. It is acceptable that the angle of rotation of the steered motor5is detected and compared by operating only the reaction motor3. In the first to fifth embodiments, torque T generated by each of the motors is configured within a range such that the steered wheels20are not steered. InFIG. 6, a torque that can steer the steered wheels20is added and the initial monitoring control is carried out based on the changes in the actual steered angle and steering angle.

FIG. 9is a flow chart showing the initial monitoring control process according to the sixth embodiment.

Steps S601to S603are the same as steps S101to S103in the flow chart ofFIG. 3.

At step S604, only the steered motor5is turned on and the process advances to step S605.

At step S605, it is determined whether the angle θ2/r that is the rotation of the reaction motor by the rotation of the steered motor5is the predetermined value Nθ2or greater. If it is YES, the process advances to step S606, and if it is NO, the process advances to step S609.

At step S606, the steered motor5is turned off and the process advances to step S607.

Steps S607and S608are the same as steps S107and108ofFIG. 3.

At step S609, the steered motor5is turned off and the process advances to step S610.

In the sixth embodiment, the steered motor5is rotated first, and the predetermined value Nθ2that corresponds to the rotation angle θ2of this steered motor5, and the rotation angle θ1of the reaction motor3that is rotated via the backup mechanism7are compared, and it is determined whether the angle θ2/r of the rotation of the reaction motor3due to the rotation of the steered motor5is the predetermined value Nθ2or greater.

If Θ2/r is the predetermined value Nθ2or greater, it is determined that the torque transmission between the steering side and the steered side via the backup mechanism7can be carried out normally and the normal steer-by-wire control is executed. If it is less than the predetermined value Nθ2, then it is determined that the torque transmission via the backup mechanism7cannot be carried out normally, and the fail-safe process is carried out as in the other embodiments.

Initial monitoring is carried out by using an inexpensive rotation sensor and therefore cost can be reduced. In addition, by combining with initial monitoring, depending on the vehicle, the effect of the first to third embodiments can also be obtained.

Initial monitoring can be carried out based on the steering angle sensor8; that is, the rotation angle of the steering shaft2closer to the driver instead of the motor rotation angle. By doing so, whether manual steering is secured can be monitored even more securely.

The initial monitoring process has been described based on the first to six embodiments. By combining embodiments, depending on the vehicle, the reliability of the initial monitoring can be further improved.

The present vehicle steering apparatus has been described by referring to six embodiments. Nonetheless, the detailed structure is not limited to these embodiments, and design changes and modifications are permitted, as long as they do not exceed the scope of the appended claims.

For example, in the embodiments described, an electromagnetic clutch is used; nonetheless, a friction-type clutch can be used. In addition, in the first embodiment, torque is added to each of the steering side and steered side motors in directions such that each of the torques offset each other, and whether the backup mechanism is normal/abnormal is determined based on the error value of the detected value of the steering side and steered side torque sensors. Nonetheless, the normal/abnormal condition can be determined by the rotation angles of the steering side and steered side.

In addition in the embodiments described, the normal/abnormal condition of the backup mechanism is determined when the ignition is turned on. Nonetheless, it can be determined when the power of the steer-by-wire system is turned on, and initial monitoring can be started by turning the power on at the release of the door lock and opening of the door at the driver's side.