Vehicle steering apparatus

Abstract: A vehicle steering apparatus comprising a driver's hand free state detecting means for detecting a driver's hand free state when returning of a steering operating means (2) to its neutral position, for controlling a reaction force to be applied to the steering operating means (2) a steering operating angle of the steering operating means (2) or a returning angular speed of the steering operating means (2), on the basis of the detection signal issued from the driver's hand free state detecting means. The driver's hand free state detecting means detects a driver's hand free state on the basis of at least vehicle speed and steering torque.

Description: The present invention relates to a vehicle steering apparatus for steering a vehicle by means of a steering mechanism which is not mechanically linked to steering operating means in response to driver's operation. Steering for vehicle is carried out in such a manner that operation of a steering operating means disposed inside a cabin of the vehicle, for example, rotation of a steering wheel is transferred to a steering mechanism disposed outside the cabin for directing wheels for steering (front wheels in general). In recent years, a power steering apparatus is widely spread. The power steering apparatus has such a structure that actuators for assisting steering such as hydraulic cylinder, and electric motor are disposed on the midway of the steering mechanism, these actuators are driven on the basis of detection results of an operational force applied to the steering wheel for steering, and operation of the steering mechanism in response to the rotation of the steering wheel is assisted by the force produced by the actuators, whereby a driver's load of labor for steering is reduced. However, in such conventional vehicle steering apparatus, it is required to link mechanically the steering wheel being a steering operating means to the steering mechanism, so that there is such a problem that a position where the steering wheel is disposed inside the cabin is restricted to that at which it can be linked to the steering mechanism disposed outside the cabin. Furthermore, even if the steering wheel is placed at a linkable position to the steering mechanism disposed outside the cabin, a complicated connecting structure is required for realizing a satisfactory linking, and it results in a factor for obstructing the light weight of vehicle and simplification of assembling steps of vehicle. In JP 2 290 17U (1990), a vehicle steering apparatus which is a power steering apparatus without linkage for the purpose of eliminating the above described problems is disclosed. This vehicle steering apparatus is constructed in such that a steering wheel is disposed separately from a steering mechanism, while an electric motor is disposed on the midway of the steering mechanism as an actuator for steering as similar to an actuator for assisting steering in a power steering apparatus. In this construction, the electric motor is driven on the basis of the detection results of an operational direction and an operation amount of the steering wheel, whereby steering is carried out in response to the operation of the steering wheel. To the steering wheel which is not linked mechanically to the steering mechanism is attached a reaction force actuator provided with a motor. The reaction force actuator drives the motor on the basis of the detection results of a vehicle speed and a steering operating angle of the steering wheel, whereby a reaction force for directing the steering wheel to its neutral position, which increases or decreases in response to an amount of vehicle speed (high or low) and a magnitude of steering operating angle (large or small) is applied to the steering wheel. In such vehicle steering apparatus, a torque which is applied to the steering wheel against the reaction force is detected, a motor current in the electric motor for steering is increased and decreased in response to the results detected thereby increasing and decreasing the steering force to be produced by the electric motor. Thus, in the above described vehicle steering apparatus steering can be carried out in the same feeling as that of a usual vehicle steering apparatus (linked type steer apparatus) wherein the steering wheel is mechanically linked to the steering mechanism. The separate type vehicle steering apparatus constructed as described is useful for developing motor vehicle technology in the future in connection with realization of a novel steering operating means such as lever, and pedal in place of an existing steering wheel; and realization of an automatic driving system with using traveling information such as detection of guide mark on road, reception of satellite information or the like, in addition to the above-mentioned purposes for achieving increase in flexibility for locating steering wheel, light weight of vehicle body and the like. US 5 347 458 A describes a similar vehicle steering apparatus corresponding to the precharacterizing part of claim 1. Said steering apparatus comprises a steer-by-wire mechanism with an operating means, an actuator for producing a reaction force acting on the steering operating means, and a steering angle detecting means for detecting the actual steering angle of the vehicle. The reaction force is calculated on the basis of the angular acceleration of the steering wheel, the angular velocity of the steering wheel, and the amount of angular displacement of the steering wheel. In the separate type vehicle steering apparatus, however, when a driver looses his (or her) holding on steering wheel in case wheels return to their neutral positions (straight traveling position) during traveling due to self-aligning torque, a torque to be applied to the steering wheel against the above-mentioned reaction force disappears, and as a result, only the reaction force directing to the neutral position is applied to the steering wheel. Hence, the steering wheel returns rapidly in this case, so that driver's steering feeling becomes different from that of a conventional steering apparatus. As a means for rotatively controlling steering wheel in case a driver looses his (or her) holding on the steering wheel, a vehicle steering apparatus for affording a damping torque to the steering wheel for suppressing vibrations due to a road situation and a control system involved in the vehicle steering apparatus in case of a driver's hand free state is proposed (JP 4 176 781 A (1992)). However, this apparatus is a means for suppressing influences derived from a road situation and the control system in case of a driver's hand free state. The present invention has been devised to solve the above problems. An object of the present invention is to provide a vehicle steering apparatus by which natural returning of a steering operating means to its neutral position which follows returning of wheels to their neutral positions due to a self-aligning torque is realized. A vehicle steering apparatus according to the present invention is characterized by the features listed in claim 1. According to this vehicle steering apparatus, when a driver looses his (or her) holding on a steering operating means in the case where the wheels return to their neutral positions (straight traveling position) during traveling due to a self-aligning torque and as a result, the steering operating means returns to its midpoint (neutral position), the driver's hand free state detecting means detects this driver's hand free state. The reaction force stopping means stops reaction force control of the steering operating means on the basis of a detection signal from the driver's hand free state detecting means, while the steering operating angle control means controls a steering operating angle of the steering operating means on the basis of a steering angle signal from the steering angle detecting means. Thus, natural returning of the steering wheel to its neutral position which follows returning of the wheels to their neutral position due to self-aligning torque can be realized. According to this vehicle steering apparatus, the above-mentioned natural returning of the steering operating means to its neutral position can be realized on the basis of the steering angle of the steering mechanism and vehicle speed. The above-mentioned natural returning of the steering operating means to its neutral position can be realized on the basis of the steering angle of the steering mechanism, the vehicle speed, and the steering operating angle of the steering operating means. According to the invention, returning of the steering operating means is also controlled by means of control for the reaction force without conducting separately the returning control as in the case mentioned above, so that the process is simplified, and as a result more natural returning is realized. Another object of the present invention is to provide a vehicle steering apparatus by which a driver's hand free state can be accurately detected. The driver's hand free state detecting means preferably includes a speed comparing means for comparing the moving speed detected by the vehicle speed detecting means with a predetermined speed; and a torque comparing means for comparing the steering torque detected by the steering torque detecting means with a predetermined value, wherein the driver's hand free state detecting means detects a driver's hand free state in the cases where the moving speed is higher than the predetermined speed arid where the steering torque is smaller than the predetermined value. According to the above, a driver's hand free state can accurately be detected on the basis of vehicle speed and steering torque. Moreover, the driver' s hand free state detecting means is preferably characterized by further including a reaction force comparing means for comparing the reaction force to be afforded to the steering operating means with a predetermined value in addition to the above described both comparing means, wherein the driver's hand free state detecting means detects a driver's hand free state in the cases where the moving speed is higher than the predetermined speed, where the steering torque is smaller than the predetermined value, and where the reaction force to be applied to the steering operating means is larger than the predetermined value. According to the above, a driver's hand free state can accurately be detected on the basis of the vehicle speed, the steering torque, and the reaction force to be afforded to the steering operating means. Moreover, the driver's hand free state detecting means in the vehicle steering apparatus may be further characterized by further including a speed comparing means for comparing a moving speed with a predetermined speed; a torque comparing means for comparing a steering torque with a predetermined value; a differentiating means for differentiating the steering torque; and a differential value comparing means for comparing the differentiated value with a predetermined value, wherein the driver's hand free state detecting means detects a driver's hand free state in the cases where the moving speed is higher than the predetermined speed, where the steering torque is smaller than the predetermined value, and where the differentiated value is larger than the predetermined value. According to the above, a driver's hand free state can accurately be detected on the basis of the vehicle speed, the steering torque, and changes in the steering torque. The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. FIG. 1 is a block diagram showing the whole construction of a vehicle steering apparatus according to the present invention; FIG. 2 is a flowchart illustrating a processing procedure of operation in the vehicle steering apparatus according to the present invention; FIG. 3 is a flowchart illustrating a processing procedure of the routine for detecting a driver's free hand state in the vehicle steering apparatus according to Embodiment 1; FIG. 4 is a flowchart illustrating a processing procedure of the routine for returning control in the vehicle steering apparatus according to Embodiment 1; FIG. 5 is a flowchart illustrating a processing procedure of the routine for reaction force control of the vehicle steering apparatus according to Embodiment 1; FIG. 6 is a flowchart illustrating a processing procedure of the routine for detecting a driver's free hand state in the vehicle steering apparatus according to Embodiment 2; FIG. 7 is a flowchart illustrating a processing procedure of the routine for returning control in the vehicle steering apparatus according to Embodiment 2; FIG. 8 is a flowchart illustrating a processing procedure of operation in the vehicle steering apparatus according to Embodiment 3; FIG. 9 is a flowchart illustrating a processing procedure of the routine for detecting a driver's free hand state in the vehicle steering apparatus according to Embodiment 3; and FIG. 10 is a flowchart illustrating a processing procedure of the routine for correcting a reaction force for instruction torque in the vehicle steering apparatus according to Embodiment 3. DETAILED DESCRIPTION OF THE INVENTION The invention will be described in detail hereinafter by referring to the accompanying drawings illustrating the examples thereof. EMBODIMENT 1. FIG. 1 is a block diagram showing the whole construction of the vehicle steering apparatus according to the present invention. This vehicle steering apparatus has a structure which is provided with a steering mechanism 1 to effect steering operation for a pair of wheels 10, 10 disposed on the opposite sides of the vehicle body; a steering wheel 2 being a steering operating means located with no mechanical connection with the steering mechanism 1; a reaction force actuator 3 for applying a reaction force to the steering wheel 2; and a steering control unit 4 comprising a microprocessor; and which actuates the steering mechanism 1 in such a manner that a steering motor 5 disposed on the midway of the steering mechanism 1 is driven by the action of the steering control unit 4 in response to the operation of the steering wheel 2. The steering control unit 4 in this embodiment includes a driver's hand free state detecting means for detecting a driver's hand free state, a reaction force stopping means for stopping reaction force control of the steering operating means, a steering operating angle control means for controlling a steering operating angle of the steering operating means, a speed comparing means for comparing a moving speed with a predetermined speed, and a torque comparing means for comparing a detected steering torque with a predetermined value. As is well-known, the steering mechanism 1 is arranged in such that the opposite ends of a steering shaft 11 which extends from side to side of the vehicle body and is slidable along the axial direction thereof are linked to knuckle arms 12, 12 for supporting wheels 10, 10 by means of separate tie rods 13, 13, respectively, and the knuckle arms 12, 12 are pushed and pulled as a result of traverse sliding of the steering shaft 11 through the tie rods 13, 13, whereby the wheels 10, 10 are directed to the left and right. Such directing is carried out by converting rotation of the steering motor 5 mounted coaxially on the midway of the steering shaft 11 into sliding of the steering shaft 11 by means of a suitable motion converting mechanism. Revolving motion around the axis of the steering shaft 11 is restricted by a rotation restricting means disposed between a steering shaft housing 14 and the steering shaft 11, whereby rotation of the steering motor 5 is converted into sliding of the steering shaft 11 in the axial direction, so that steering (directing of the wheels 10, 10 for steering) is made in response to rotation of the steering motor 5. A steering angle of the wheels 10, 10 thus steering-operated is detected by a steering angle sensor 16 being a steering angle detecting means through the medium of a position of relative sliding defined by the steering shaft housing 14 and the steering shaft 11 on one side of the steering motor 5. Output of the steering angle sensor 16 is given to the steering control unit 4 together with output of a rotary encoder 15 for detecting a rotational position of the steering motor 5. The reaction force actuator 3 for applying the reaction force to the steering wheel 2 is an electric motor (for example, three-phase brushless motor) wherein the casing thereof is fixedly mounted on a suitable portion of the vehicle body in relation to a rotation shaft 30. The steering wheel 2 is coaxially secured to a protruding end on a side of the rotation shaft 30, while a protruding end on the other side is linked to a suitable portion of the vehicle body through a torsion spring 31 having predetermined elasticity. The reaction force actuator 3 is driven in reciprocal directions upon current application from a driving circuit 3a in response to a reaction force instruction torque signal given from the steering control unit 4, and which functions to give a force reverse to that of an operating direction (reaction force) to the steering wheel 2 mounted on one end of the rotation shaft 30. Accordingly, it is required to add steering torque against the reaction force generated by the reaction force actuator 3 for rotating the steering wheel 2. Thus, the steering torque applied to the steering wheel 2 is detected by a torque sensor 32 attached to the reaction force actuator 3. Furthermore, an amount of operation (a steering operating angle) including an operating direction of the steering wheel 2 is detected by a rotary encoder 33 attached to the reaction force actuator 3. These detection results are given to the steering control unit 4. Moreover, the current applied to the reaction force actuator 3 from the driving circuit 3a is detected by a current sensor 3b and given to the steering control unit 4. The torsion spring 31 disposed between the other end of the rotation shaft 30 and a part of the vehicle body functions to rotate the rotation shaft 30 due to the elasticity thereof in case of stopping the rotating operation conducted as described above, whereby the steering wheel 2 is returned to a predetermined neutral position. The returning motion is necessary for returning the steering wheel 2 in relation to the returning towards the straight driving direction of the wheels 10, 10 generated in the steering mechanism 1 mechanically separated from the steering wheel 2. As described above, to the steering control unit 4 is given a state of steering which occurs actually in the steering mechanism 1 by way of the inputs from the rotary encoder 15 and the steering angle sensor 16, besides a state of operation for the steering wheel 2 being a steering operating means is given also by way of the inputs from the torque sensor 32 and the rotary encoder 33, respectively. In addition to these inputs, an output of a vehicle speed sensor 6 for detecting a moving speed of the vehicle is given to the input side of the steering control unit 4. On the other hand, the output of the steering control unit 4 is sent to the reaction force actuator 3 for applying the reaction force to the steering wheel 2 and the steering motor 5 for steering action in the steering mechanism 1 through the respective separate driving circuits 3a, 5a, whereby the reaction force actuator 3 and the steering motor 5 act separately in response to instruction signals from the steering control unit 4. The steering control unit 4 decides the reaction force to be applied to the steering wheel 2 so as to become large or small in response to, for example, a magnitude of moving speed (low or high) given as an input from a vehicle speed sensor 6, whereby the reaction force control of issuing reaction force instruction torque signal to the reaction force actuator 3 is conducted for generating the reaction force. Furthermore, the steering control unit 4 recognizes an operation angle including an operating direction of the steering wheel 2 by means of the input from the rotary encoder 33 to calculate a steering angle deviation defined between the operation angle and an actual steering angle recognized by the input of the steering angle sensor 16 provided on the steering mechanism 1. Then, it corrects the steering angle deviation in such that it becomes larger or smaller in response to the magnitude of the vehicle speed (low or high) given from the vehicle sensor 6 as input to determine a target steering angle. And steering control action for driving the steering motor 5 is carried out until the target steering angle is obtained. In this case, the input from the rotary encoder 15 is utilized for feedback signal for examining whether the steering motor 5 reaches a desired rotational position or not. Operation of a vehicle steering apparatus having the construction as described above will be explained hereinafter with reference to flowcharts illustrating such operation. FIG. 2 is a flowchart illustrating a processing procedure for operation of the vehicle steering apparatus according to Embodiment 1. The steering control unit 4 practices periodically such a routine that a state in which a driver looses his (or her) holding on the steering wheel 2 is detected on every occasion when the wheels return to their neutral positions (straight traveling position) due to self-aligning torque during traveling of the vehicle, and as a result, the steering wheel 2 returns to its neutral position (R2). When such driver's hand free state is not detected (R4), the above-mentioned routine for the reaction force control is executed (R8). When the driver's hand free state is detected (R4), the reaction force control is not executed, but a routine for returning control of the steering wheel 2 is executed (R6). FIG. 3 is a flowchart illustrating in detail a processing procedure of the routine (R2) for detecting the driver's hand free state of Embodiment 1. The steering control unit 4 reads in the vehicle speed from the vehicle speed sensor 6 (S2), when the vehicle speed is a predetermined value or more (S4), the steering control unit 4 gains the steering torque of the steering wheel 2 from the torque sensor 32 (S6). When the obtained steering torque (S6) is a predetermined value or less (S8), it is judged that there is a driver's hand free state for detecting (S10), and the procedure returns. In case either the read vehicle speed (S2) is less than the predetermined value (S4), or the read steering torque (S6) exceeds the predetermined value (S8), it is not judged that there is a driver's hand free state, and the procedure returns. In the routine for detecting a driver's hand free state (R2), while it is judged that there is a driver's hand free state in the cases where the vehicle speed is the predetermined value or more (S4), and where the steering torque is the predetermined value or less (S8), there may be added such condition as reaction force instruction torque is a predetermined value or more (a deviation defined between reaction force instruction torque and steering torque is remarkable) or as a differential value of steering torque is a predetermined value or more (rapid decrease in steering torque), in addition to the above described two conditions (S4, S8). FIG. 4 is a flowchart illustrating in detail a processing procedure for the returning control routine (R6) of Embodiment 1. When the steering control unit 4 detects the driver's hand free state (R4 in FIG. 2), it obtains the steering angle (a position of rack shaft) of the wheels 10, 10 (S12) from the steering angle sensor 16, and calculates a steering wheel target steering operating angle  M in response to the steering angle (S14). Then, the steering operating angle  S of the steering wheel 2 is detected by the rotary encoder 33 (S16), and the steering angle deviation ΔI n =  M -  S defined between the steering wheel target steering operating angle  M and the steering wheel steering operating angle  S is calculated (S18). Thereafter, an integral element I n = ΔI n ×K I (K I : predetermined integral constant) of the returning control is calculated (S20), and further, a proportional element P n = (ΔI n - ΔI n-1 )×K P (ΔI n-1 : steering angle deviation in the preceding cycle, K P : predetermined proportional constant) is calculated (S22). Then, a target voltage of an electric motor in the reaction force actuator 3 (reaction force motor target voltage) V M = V 0 + I n + P n (V 0 : a target voltage in the preceding cycle) is calculated (S24) to output the target voltage V M from the driving circuit 3a, whereby the electric motor of the reaction force actuator 3 is driven. Thereafter, the target voltage V M and the steering angle deviation ΔI n are transferred to the target voltage V 0 in the preceding cycle and to the steering angle deviation in the preceding cycle ΔI n-1 , respectively (S26), and the procedure returns. FIG. 5 is a flowchart illustrating in detail a processing procedure for the reaction force control routine (R8) of Embodiment 1. When a driver's hand free state is not detected by the steering control unit 4 (R4 in FIG. 2), it reads in the reaction force instruction torque T M corresponding to a steering operating angle  S of the steering wheel 2 detected by the rotary encoder 33 from a table of the reaction force instruction torque relative to a steering operating angle (S30), and the steering torque T S is detected by the torque sensor 32 (S32). Then, a torque deviation ΔD n = T M - T S defined between the reaction force instruction torque T M and the steering torque T S is calculated (S34), and an integral element Dn = ΔD n ×K I2 of reaction force control (K I2 : predetermined integral constant) is calculated (S36). Thereafter, a proportional element P n = (ΔD n - ΔD n-1 ) × K P2 (ΔD n-1 : torque deviation in the preceding cycle, K P2 : predetermined proportional constant) is calculated (S38), and a target current of the electric motor in the reaction force actuator 3 (reaction force motor target current) J M = J 0 + D n + P n (J 0 : target current in the preceding cycle) is calculated (S40). Thereafter, a current J S of the electric motor in the reaction force actuator 3 is detected by the current sensor 3b (S42), and a current deviation ΔD n ' = J M - J s defined between the target current J M and the actual current J s in the electric motor is calculated (S44). Then, the steering control unit 4 calculates an integral element D n ' = ΔD n ' ×K 12 ' (K I2 : predetermined integral constant), and calculates a proportional element P n ' = (ΔD n ' - ΔD n-1 ')×K P2 ' (ΔD n-1 ' : current deviation in the preceding cycle, K P2 ': predetermined proportional constant) (S48). Then, a target voltage of the electric motor in the reaction force actuator 3 (reaction force motor target voltage) V M = V 0 + D n ' + P n ' (V 0 : a target value of the preceding cycle) is calculated (S50) to output the target voltage V M from the driving circuit 3a, whereby the electric motor of the reaction actuator 3 is driven. Thereafter, the target current J M , the target voltage V M , the torque deviation ΔD n , and the current deviation ΔD n ' are transferred to the target current J 0 in the preceding cycle, the target voltage V 0 in the preceding cycle, the torque deviation in the preceding cycle ΔD n-1 , and the current deviation in the preceding cycle ΔD n-1 ', respectively (S52), and the procedure returns. Embodiment 2. The construction of the vehicle steering apparatus and the operation other than the routine for detecting a driver's hand free state and that for returning control according to the present example are the same as those of Embodiment 1, so that the explanation therefor will be omitted. Wherein the steering control unit 4 includes a driver's hand free state detecting means for detecting a driver's hand free state, a reaction force stopping means for stopping reaction force control of the steering operating means, a steering operating angle speed control means for controlling a returning angular speed in steering operating angle of the steering operating means, a steering angle control means for controlling to reduce a steering angle of the steering mechanism, a speed comparing means for comparing a moving speed with a predetermined speed, and a torque comparing means for comparing a detected steering torque with a predetermined value. FIG. 6 is a flowchart illustrating in detail the routine (R2 in FIG. 2) for a processing procedure of the driver's hand free state according to Embodiment 2. The steering control unit 4 obtains a vehicle speed from the vehicle speed sensor 6 (S80), and when the vehicle speed is a predetermined value or more (S82), it reads in a steering torque of the steering wheel 2 from the torque sensor 32 (S84). When the read steering torque is a predetermined value or less (S86), the steering control unit 4 gets a reaction force instruction torque corresponding to a steering operating angle of the steering wheel 2 (S88). When the obtained reaction force instruction torque is a predetermined value or more (S90), the steering control unit 4 judges that there is a driver's hand free state to detect the same (S92), and the procedure returns. When there is any one of the cases where the read vehicle speed (S80) is the predetermined value or less (S82), where the obtained steering torque (S84) exceeds the predetermined value (S86), or where the read reaction force instruction torque is less than the predetermined value (S90), the steering control unit 4 does not judge that there is a driver's hand free state, and the procedure returns. In other words, the steering control unit 4 judges that there is a driver's hand free state in the cases when the vehicle speed is the predetermined value or more (S82), when the steering torque is the predetermined value or less (S86), and when the reaction force instruction torque is the predetermined value or more (S90) (a deviation defined between the reaction force instruction torque and the steering torque is significant). It is to be noted that such a condition that a differential value of steering torque is a predetermined value or more (rapid decrease in steering torque) may be added in place of the condition to the effect that the reaction force instruction torque is the predetermined value or more (S90) mentioned above. FIG. 7 is a flowchart illustrating in detail a processing procedure for the returning control routine (R6 in FIG. 2) according to Embodiment 2. When a driver's hand free state is detected (R4 in FIG. 2), the steering control unit 4 reads in a steering angle of the wheels 10, 10 (steering mechanism) from the steering angle sensor 16, and further a moving speed of the vehicle from the vehicle speed sensor 6 (S56), whereby a target steering operating angular speed d M of the steering wheel 2 is calculated on the basis of the read steering angle and the moving speed (S58). Then, the steering control unit 4 detects a steering operating angular speed d S of the steering wheel 2 from changes in the steering operating angle  S of the steering wheel 2 detected by the rotary encoder 33 (S60), and calculates a steering operating angular speed deviation ΔH n = d M - d S defined between the target steering operating angular speed d M and the actual steering operating angular speed d S of the steering wheel 2 (S62). Thereafter, an integral element of returning control H n = ΔH n ×K I3 (K I3 : predetermined integral constant) is calculated (S64), and further a proportional element P n = (ΔH n - ΔH n-1 ) × K P3 (ΔH n-1 : steering operating angular speed deviation in the preceding cycle, K P3 : predetermined proportional constant) is calculated (S66). Then, a target voltage of the electric motor in the reaction force actuator 3 (reaction force motor target voltage) V M = V 0 + H n + P n (V 0 : target value in the preceding cycle) is calculated (S68) to output the target voltage V M from the driving circuit 3a, whereby the electric motor of the reaction force actuator 3 is driven. Thereafter, the target voltage V M , and the steering operating angular speed deviation ΔH n are transferred to the target voltage V 0 in the preceding cycle, and the steering operating angular speed deviation in the preceding cycle ΔH n-1 , respectively (S70). Thereafter, the steering control unit 4 controls to reduce the steering angle of the wheels 10, 10 (steering mechanism) on the basis of the steering operating angle  S of the steering wheel 2 (S72) detected by the rotary encoder 33 (S60), and the procedure returns. Embodiment 3. The construction of the vehicle steering apparatus and the routine for reaction force control according to Embodiment 3 are the same as the construction and the reaction force control routine (R8 in FIG. 2) of Embodiment 1, so that the explanation therefor will be omitted. Wherein the steering control unit 4 includes a driver's hand free state detecting means for detecting a driver's hand free state, a correcting means for correcting to reduce a reaction force to be applied to the steer operation means on the basis of a detection signal of the driver's hand free state detecting means in response to a steering angle signal of the steering angle detecting means, a speed comparing means for comparing a moving speed with a predetermined speed, a torque comparing means for comparing a detected steering torque with a predetermined value, a differential value comparing means for comparing the value obtained by differentiating the steering torque with a predetermined value. FIG. 8 is a flowchart illustrating a processing procedure for operation of the vehicle steering apparatus according to Embodiment 3. The vehicle steering apparatus of the present example practices periodically such a routine that a state in which a driver looses his (or her) holding on the steering wheel 2 is detected in the case where the wheels returns to their neutral positions (straight traveling position) due to self-aligning torque during traveling of the vehicle, and as a result, the steering wheel 2 returns to its neutral position (R3). When a driver's hand free state is not detected (R4), the above-mentioned routine for reaction force control is executed (R8). When a driver's hand free state is detected (R4), after correcting an instruction torque for reaction force control (R7), the reaction force control is executed (R8). FIG. 9 is a flowchart illustrating in detail a processing procedure of the routine (R3 in FIG. 8) for detecting a driver's hand free state of Embodiment 3. The steering control unit 4 reads in a vehicle speed from the vehicle speed sensor 6 (S94), when the vehicle speed is a predetermined value or more (S96), the steering control unit 4 obtains steering torque of the steering wheel 2 from the torque sensor 32 (S98). When the read steering torque is a predetermined value or less (S100), a difference defined between the steering torque in case of the preceding sampling cycle and the steering torque in this time is determined to be differentiated (S102). When (an absolute value of) a differential value of the steering torque is a predetermined value or more (S104), the steering control unit 4 judges that there is a driver's hand free state to detect the same (S106), and the procedure returns. On the other hand, the steering control unit 4 does not judge that there is a driver's hand free state in any one of the cases where the obtained vehicle speed (S94) is the predetermined value or less (S96), where the obtained steering torque (S98) exceeds the predetermined value (S100), and where the differential value of the steering torque (S102) is less than the predetermined value (S104), and the procedure returns. In other words, the steering control unit 4 judges that there is a driver's hand free state in case the vehicle speed is the predetermined value or more (S96), the case when the steering torque is the predetermined value or less (S100), and the case when the differential value of the steering torque is the predetermined value or more (S104) (rapid decrease in steering torque). It is to be noted that such a condition that a reaction force instruction torque is a predetermined value or more (a deviation defined between the reaction force instruction torque and a steering torque is significant) may be added in place of the above-mentioned condition to the effect that the differential value of steering torque is the predetermined value or more (S104). FIG. 10 is a flowchart illustrating in detail a processing procedure for correcting the instruction torque routine (R7) according to Embodiment 3. When a driver's hand free state is detected (R4 in FIG. 8), the steering control unit 4 reads in a steering angle of the wheels 10, 10 (steering mechanism) from the steering angle sensor 16 (S74), and it reduces to correct the reaction force instruction torque on the basis of the obtained steering angle (S76). Then, the procedure returns. The steering control unit 4 executes the reaction force controlling routine (FIG. 5) based on the reaction force instruction torque reduced and corrected. It is to be noted that the vehicle steering apparatus in the above described Embodiments shows a mere example of the present invention, so that the structures of the reaction force actuator 3 and the steering motor 5 are not limited thereby. As a matter of course, other operating means than the steering wheel 2, for example, lever, joy stick and the like may be used as the steering operating means in the present invention. According to the vehicle steering apparatus of the present invention, natural returning to the neutral position of steering wheel which follows the returning to the neutral position of wheels due to self-aligning torque can be realized. Furthermore, a driver's hand free state can be detected precisely in the present invention, and natural returning to the neutral position of steering wheel following the returning to the neutral positions of wheels due to self-aligning torque can be realized in case of a driver's hand free state.

Claims: A. vehicle steering apparatus, comprising a steering mechanism (1) being not mechanically connected with a steering operating means (2) for steering wheels (10) on the basis of a control amount supplied from said steering operating means (2) for controlling a reaction force to said steering operating means (2) by driving a reaction force motor (3) on the basis of a steering control amount of said wheels (10), said steering mechanism comprising a steering angle detecting means (16) for detecting a steering angle of said steering mechanism (1), characterized in that it comprises a driver's hand free state detecting means (4) for detecting a driver's hand free state in case said steering operating means (2) returns to its neutral position, and a means (4) for correcting a reaction force to be applied to said steering operating means (2) in response to a steering angle signal of said steering angle detecting means (16) by reducing said reaction force, or for stopping reaction force control with respect to said reaction force motor (3), on the basis of the detection signal from said driver's hand free state detecting means (4). The vehicle steering apparatus as claimed in claim 1, further comprising a steering operating angle control means (4) for controlling a steering operating angle of said steering operating means (2) on the basis of a steering angle signal of said steering angle detecting means (16) during stopping reaction force control for said steering operating means (2). The vehicle steering apparatus as claimed in claim 1 or 2, further comprising: a vehicle speed detecting means (6) for detecting a moving speed of the vehicle, and a steering operating angular speed control means (4) for controlling a returning angular speed in steering operating angle of said steering operating means (2) on the basis of a vehicle speed signal of said vehicle speed detecting means (6) and a steering angle signal of said steering angle detecting means (16) during stopping reaction force control for said steering operating means. The vehicle steering apparatus as claimed in any of claims 1-3, further comprising a steering torque detecting means (32) for detecting a steering torque applied to said steering operating means (2), wherein said driver's hand free state detecting means (4) includes: a speed comparing means (4) for comparing the moving speed detected by said vehicle speed detecting means (6) with a predetermined speed, and a torque comparing means (4) for comparing the steering torque detected by said steering torque detecting means (32) with a predetermined value, and said driver's hand free state detecting means (4) detects said driver's hand free state in the case where said moving speed is higher than the predetermined speed and where said steering torque is smaller than the predetermined value. The vehicle steering apparatus as claimed in claim 4, further comprising a reaction force comparing means (4) for comparing a reaction force to be applied to said steering operating means (2) with a predetermined value. The vehicle steering apparatus as claimed in claim 4, further comprising a reaction force comparing means (4) for comparing a reaction force to be applied to said steering operating means (2) with a predetermined value. The vehicle steering apparatus as claimed in claim 4, wherein said driver's hand free state detecting means (4) includes: a differential means (4) for differentiating the steering torque detected by said steering torque detecting means (32), and a differential value comparing means (4) for comparing the value obtained by differentiating said steering torque by said differential means (4) with a predetermined value.

Inventors: KATO TAKAYUKI, KAWAGUCHI HIROSHI, NISHIMOTO MITSUHIKO, KATO, TAKAYUKI, KAWAGUCHI, HIROSHI, NISHIMOTO, MITSUHIKO
Applicants: KOYO SEIKO CO, KOYO SEIKO CO., LTD.
Application year: 1998
Main classification: B62D6
IPC codes: B62D5, B62D6, B62D113, B62D101