JP4221656B2 - Vehicle steering system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle steering apparatus including a plurality of motors for driving a steering shaft extending in the left-right direction of the vehicle.
[0002]
[Prior art]
2. Description of the Related Art In recent years, as a power steering device for a vehicle, an electric type instead of a hydraulic type has been widely used. For example, in order to obtain a steering assist force comparable to that of a hydraulic actuator, a plurality of electric motors arranged in parallel with a rack shaft as a steering shaft are provided, and the rack shaft is pivoted from each electric motor via a steering gear on the steering shaft. There has been provided an electric power steering device that assists driving in a direction (for example, Patent Document 1).
[0003]
Further, in a so-called steer-by-wire vehicle steering apparatus in which a steering wheel as a steering means is arranged without being mechanically connected to a steering mechanism, a rack is provided via a main steering motor on a rack shaft and a pinion. There has been proposed a vehicle steering device that is provided with a sub-steering motor that applies a steering force to the shaft, is normally steered by the resultant force of both motors, and that is steered only by a normal motor when an abnormality occurs in either motor ( For example, Patent Document 2).
[0004]
[Patent Document 1]
JP-A-5-155343 [Patent Document 2]
Japanese Patent Laid-Open No. 10-218000
[Problems to be solved by the invention]
However, when using a plurality of motors, for example, as in Patent Document 1, these motors all require a large space on the side of the rack shaft, or, as in Patent Document 2, one motor is a rack. It overhangs in a direction substantially perpendicular to the axis. For this reason, there has been a problem that layout of parts around the rack shaft becomes difficult.
[0006]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a vehicle steering apparatus in which the layout of components around the steering shaft is easy.
[0007]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, a first aspect of the present invention is a vehicle steering apparatus comprising a plurality of motors for driving a steering shaft extending in the left-right direction of the vehicle, wherein the plurality of motors face the axial direction of the steering shaft. and and respectively enclose take a steering shaft concentrically, the rotation of each motor rotor comprising a plurality of motion converting mechanism for converting the respective axial movement of the steering shaft, the motion converting mechanism of the corresponding motor Each of the rotors includes a rotating cylinder that can rotate integrally with the rotor and surrounds the periphery of the steering shaft, and an elastic member is interposed between the adjacent rotating cylinders . In the present invention, a plurality of motors are laid out compactly around the steering shaft, and there is no concern about interference with surrounding parts.
[0008]
Further, the rotation of each motor rotor comprising a plurality of motion converting mechanism for converting the respective axial movement of the steering shaft, the periphery of each motion converting mechanism is integrally rotatable with the rotor of the corresponding motor steering shaft Since each of the surrounding rotating cylinders is included and an elastic member is interposed between adjacent rotating cylinders , the following advantages are obtained. In other words , in the present invention, adjacent rotating cylinders are preloaded in opposite directions and axial backlash can be eliminated. As a result, the response of driving the steering shaft by the motor is improved.
[0009]
The second invention is characterized in that, in the first invention, the plurality of motors includes either a common stator or a common rotor. In the present invention, the manufacturing cost can be significantly reduced by the common use of the members.
The third invention is the first or the second aspect, that the plurality of motors comprises a common rotor rotation angle detecting means, characterized in that it is driven on the basis of a detection signal of the rotor rotation angle detector It is. In the present invention, the manufacturing cost can be significantly reduced by commonly using a rotor rotation angle detection means such as a resolver for a plurality of motors.
[0010]
The fourth invention is the first or the second aspect, wherein the plurality of motor rotor rotation angle detecting means, respectively, based on the comparison of the detection signal of the rotor rotation angle detector of the plurality of motors, the rotor rotation angle detector The apparatus further includes means for determining abnormality of the means or the motor. In this invention, there exist the following effects. That is, if an abnormality is determined based on the current value of the motor, the motor load has already increased when the abnormality is determined. On the other hand, in the present invention, since abnormality is determined based on the detection signal of the rotor rotation angle detection means for motor control, for example, abnormality can be quickly determined when the motor load does not increase so much. .
According to a fifth aspect of the present invention, in the vehicle steering apparatus including a plurality of motors for driving a steering shaft extending in the left-right direction of the vehicle, the plurality of motors face each other in the axial direction of the steering shaft, and the steering shafts are concentric with each other. And the plurality of motors each include a rotor rotation angle detection means, and a rotor rotation angle detection means or a means for determining abnormality of the motor based on comparison of detection signals of the rotor rotation angle detection means of the plurality of motors. Further, the plurality of motors are two motors, and the rotor rotation angle detection means or the means for determining motor abnormality includes means for calculating a difference between detection signals of the rotor rotation angle detection means included in each motor; A first comparison unit that compares the calculated difference with a first threshold, a second comparison unit that compares the calculated difference with a second threshold value greater than the first threshold, and a first comparison unit. Based on the comparison result it is characterized in that including the abnormality determination means for determining an abnormality of the motor based on the comparison result by the second comparison means with determining the abnormality of the rotor rotation angle detector.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering apparatus according to a first embodiment of the present invention. With reference to FIG. 1, in the present embodiment, the vehicle steering apparatus will be described based on an electric power steering apparatus (EPS) 1. However, the present invention is not limited to this, for example, a steering wheel or the like. It can also be applied to a so-called steer-by-wire (SBW) system in which the mechanical coupling between the steering member 2 and the steering mechanism is eliminated.
[0012]
The electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2, a pinion 4 connected to the steering shaft 3 via an intermediate shaft 100, and a rack 5 that meshes with the pinion 4. It has a rack shaft 6 as a steering shaft extending in the left-right direction.
Tie rods 7 are coupled to both ends of the rack shaft 6, and each tie rod 7 is connected to a corresponding wheel 8 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted by the pinion 4 and the rack 5 into a linear motion of the rack shaft 6 along the left-right direction of the vehicle. Thereby, steering of the wheel 8 is achieved.
[0013]
The steering shaft 3 is divided into an input shaft 9 connected to the steering member 2 and an output shaft 10 connected to the pinion 4. These input and output shafts 9 and 10 are mutually connected on the same axis line via a torsion bar 11. It is connected.
A torque sensor 12 is provided for detecting a steering torque based on a relative rotational displacement amount between the input and output shafts 9 and 10 via the torsion bar 11, and a torque detection result of the torque sensor 12 is obtained from a control unit (electronic control unit: ECU ). The control unit 13 controls the current supplied to the steering assisting electric motors 17 and 18 via the separate drivers 15 and 16 based on the torque detection result, the vehicle speed detection result from the vehicle speed sensor 14 and the like. . The control unit 13 includes a CPU 13a, a ROM 13b that stores a control program, a RAM 13c that is used as a work area, and the like.
[0014]
The output rotations of the electric motors 17 and 18 are converted into axial movements of the rack shaft 6 via motion conversion mechanisms 19 and 20 such as corresponding ball screw mechanisms, respectively, and steering is assisted. The electric power steering apparatus 1 is a so-called rack assist type.
The electric motors 17 and 18 are, for example, brushless motors, are adjacent to each other in the axial direction of the rack shaft 6, and are disposed so as to concentrically surround the rack shaft 6.
[0015]
The electric motors 17 and 18 are rotatably supported via cylindrical stators 22 and 23 fixed to the inner periphery of the rack housing 21 and bearings 24 and 25 corresponding to the rack housing 21, respectively. And rotors 26 and 27 inserted into 22 and 23, respectively. Although not shown in the drawing, a coil composed of a plurality of excitation phases that winds part of the stators 22 and 23 is provided, and the outer circumferences of the rotors 26 and 27 are opposed to the stators 22 and 23. A cylindrical driving magnet is provided. The driving magnet is magnetized so as to alternately form N and S poles in the circumferential direction.
[0016]
The electric motors 17 and 18 are provided with resolvers 41 and 42 for detecting the rotational positions (rotation angles) of the rotors 26 and 27, respectively. Each resolver 41, 42 includes a stator portion 43 fixed to the rack housing 21 and a rotor portion 44 that rotates integrally with the corresponding rotor 26, 27. Since a predetermined voltage is induced in the stator portion 43 in accordance with the rotational position of the rotor portion 44, the rotational position (phase) of the rotor portion 44, that is, the rotors 26 and 27 can be determined by measuring this voltage. .
[0017]
Based on the rotational positions (phases) of the rotors 26 and 27 output from the resolvers 41 and 42, the controller 13 divides the coils divided in the rotational direction of the stators 22 and 23 of the corresponding electric motors 17 and 18. Current is sequentially supplied and distributed to the excitation phases (not shown), and as a result, the electric motors 17 and 18 composed of brushless motors are driven and controlled to generate a predetermined rotational output.
As the motion conversion mechanisms 19 and 20, a rotational motion can be converted into a linear motion using a ball screw mechanism or a bearing screw mechanism (for example, JP 2000-46136 A). In the present embodiment, description will be made in accordance with an example in which a ball screw mechanism is used. The motion conversion mechanisms 19 and 20 have ball nuts 28 and 29 as rotating cylinders surrounding the rack shaft 6. The ball nuts 28 and 29 are screwed into a ball screw groove 6 a formed in the middle of the rack shaft 6 via a ball 30, thereby constituting motion conversion mechanisms 19 and 20.
[0018]
Corresponding ball nuts 28 and 29 are press-fitted and fixed to opposing ends of the rotors 26 and 27 of the electric motors 17 and 18, and the opposite ends of the rotors 26 and 27 are racked via corresponding bearings 24 and 25. The housing 21 is rotatably supported.
Further, the bearings 24 and 25 abut against the positioning step portions on the outer peripheral surfaces of the corresponding rotors 26 and 27, thereby restricting the movement of the corresponding rotors 26 and 27 away from each other.
[0019]
On the other hand, an elastic member 31 such as a compression coil spring or an annular rubber is interposed between the opposing ends of the ball nuts 28 and 29, and elastically biases the ball nuts 28 and 29 in a direction away from each other. As a result, the ball nuts 28 and 29 are preloaded in opposite directions so that there is no backlash in the axial direction. As a result, the responsiveness of driving the rack shaft 6 by the electric motors 17 and 18 is enhanced.
Based on the torque detection result, the vehicle speed detection result, and the like, the control unit 13 determines the control amount of the electric motors 17 and 18, and sets the electric motors 17 and 18 to the rotation angles detected by the corresponding resolvers 41 and 42. Based on this, drive control is performed so that a predetermined output is obtained.
[0020]
The driving force (rotational force of the output shaft) of the electric motors 17 and 18 is converted into linear motion in the axial direction (vehicle width direction) of the rack shaft 6 by the corresponding motion conversion mechanisms 19 and 20, thereby The required steering assist force for the steering of 8 is obtained.
According to the present embodiment, the plurality of motors 17 and 18 that are concentrically arranged on the rack shaft 6 are used so as to be opposed to each other in the axial direction of the rack shaft 6, so that the power generation unit is arranged around the rack shaft 6. Since the layout can be made compact, there is no concern about interference with surrounding parts.
[0021]
Further, the adjacent ball nuts 28 and 29 are preloaded in the opposite directions by the elastic members 31 interposed therebetween, so that axial backlash can be eliminated. As a result, the steering assist response by the electric motors 17 and 18 is improved. Become.
2 (a) and 2 (b) are schematic cross-sectional views of the main part of the vehicle steering system showing another embodiment of the present invention. In the embodiment of FIG. 2A, the plurality of electric motors 17 and 18 include a rotor unit 32 as a common rotor. The rotor unit 32 is formed by connecting rotor portions 32a and 32b respectively corresponding to the electric motors 17 and 18 via a rotating cylinder 32c such as a ball nut so as to be integrally rotatable.
[0022]
On the other hand, in the embodiment of FIG. 2B, the plurality of electric motors 17 and 18 are provided with a common long stator 33. 2 (a) and 2 (b), the same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. According to the embodiment shown in FIGS. 2A and 2B, the manufacturing cost can be remarkably reduced by sharing the members. Moreover, it can contribute to size reduction of the vehicle steering device.
Next, FIG. 3 shows still another embodiment of the present invention. In the embodiment of FIG. 3, the resolver 35 is used as a common rotor rotation angle detection means in the plurality of electric motors 17 and 18. When the electric motors 17 and 18 have rotors individually (see FIG. 1), the rotor portion of the resolver 35 is integrated with the rotor of one of the electric motors 17 and 18 (not shown in FIG. 3). What is necessary is just to attach so that it may rotate. When the rotor unit 32 shared between the electric motors 17 and 18 is used [see FIG. 2 (a)], the rotor unit of the resolver 35 may be attached to the rotor unit 32.
[0023]
In the present embodiment, the use of the resolver 35 as a common rotor rotation angle detection means for the plurality of electric motors 17 and 18 can reduce the manufacturing cost and contribute to the downsizing of the vehicle steering apparatus. be able to. Moreover, since the detection signal from the common resolver 35 should just be processed, the control load of the control part 13 can be reduced.
Next, FIG. 4 shows still another embodiment of the present invention. In the embodiment of FIG. 4, a plurality of control units (ECUs) 131 and 132 are provided as a countermeasure against failure. Similar to the embodiment of FIG. 3, a common resolver 35 is used by the plurality of electric motors 17, 18, and a detection signal from the resolver 35 is given to the control units 131, 132. Usually, only one control unit 131 is used to drive and control the plurality of electric motors 17 and 18 via different control lines a and b, but when the one control unit 131 fails, The other control unit 132 controls the driving of the electric motors 17 and 18 via the separate control lines c and d. In this embodiment, since the control system for failure is provided in a separate system, the reliability is high.
[0024]
Next, FIG. 5 shows still another embodiment of the present invention. In the embodiment of FIG. 5, output signals are given to a plurality of control units 131 and 132 via two lines e and f from resolvers 41 and 42 provided in the electric motors 17 and 18, respectively. Normally, one control unit 131 drives and controls the plurality of electric motors 17 and 18 via the separate control lines a and b using the detection signal of one resolver 41.
[0025]
When one of the resolvers 41 breaks down, the one control unit 131 drives and controls the plurality of electric motors 17 and 18 via the separate control lines a and b using the other resolver 42. Furthermore, when one control unit 131 fails, the other control unit 132 is used in the same manner as the embodiment of FIG. In the embodiment of FIG. 5, by providing a plurality of resolvers 41 and 42 and a plurality of control units 131 and 132, good control can be performed even during a failure.
[0026]
Next, FIG. 6 shows still another embodiment of the present invention. The embodiment of FIG. 6 differs from the embodiment of FIG. 5 in that a plurality of control units 131 and 132 monitor each other via a signal transmission line g and compare signals from the resolvers 41 and 42. Based on this, the failure of the resolvers 41 and 42 or the electric motors 17 and 18 is determined, and a warning is given by the notification member 50. As the notification member 50, a lamp, a liquid crystal display unit, a buzzer, or the like can be used.
[0027]
Specifically, as shown in the flowchart of FIG. 7, detection signals m1 and m2 from a plurality of resolvers 41 and 42 are input (step S1), and a difference Δm (Δm = m1−m2) is calculated ( In step S2), it is monitored whether or not the obtained difference Δm exceeds the first threshold value K1 (Δm> K1) (step S3).
When the difference Δm exceeds the first threshold value K1 (YES in step S3), the second threshold value K2 larger than the first threshold value K1 is adopted as a new threshold value, and the difference Δm becomes the second difference value. It is determined whether or not the threshold value K2 is exceeded (Δm> K2) (step S4).
[0028]
If the difference Δm exceeds the second threshold value K2 (Δm> K2) (YES in step S4), it is determined that one of the electric motors 17 or 18 is stopped, for example, by sound or display The driver is notified that an abnormality has occurred and a warning is given (step S5). Note that the change to the second threshold K2 is performed while the vehicle is traveling. The value of the first threshold value K1 is set to a value slightly larger than this phase difference in consideration of a mechanical phase difference (backlash) in the rotational direction existing between the plurality of electric motors 17 and 18.
[0029]
In the embodiment shown in FIGS. 6 and 7, abnormality is determined based on detection signals of the resolvers 41 and 42 as rotor rotation angle detection means for motor control. For example, in a stage where the motor load does not increase so much, Therefore, it is possible to determine an abnormality and to respond quickly to a failure.
On the other hand, in the conventional case where abnormality is determined based on the current value of the motor, the motor load has already increased at the time when abnormality is determined, and there is a possibility that failure handling will be delayed.
[0030]
The reason why the threshold value is set in two stages as in the above-described flowchart is to distinguish between the case of an abnormality of only the resolver as the detection means and the case of an abnormality of the electric motor itself. That is, the comparison between the difference Δm and the smaller first threshold value K1 (step S3) mainly determines the output abnormality of the resolver 41 or 42, and the comparison between the difference Δm and the larger second threshold value K2 ( In step S4), an abnormality such as disconnection of the electric motor 17 or 18 is mainly determined.
[0031]
In the embodiment of FIG. 7, the control unit that controls the abnormality may be a main control unit (ECU) that controls the entire vehicle. In this case, the detection signals of the resolvers 41 and 42 are given to the main control unit via communication means such as CAN (Controller Area Network), for example, so that the main control unit performs abnormality determination and operates the notification member. Anyway.
The present invention is not limited to the above-described embodiments, and the present invention can be applied to a so-called steer-by-wire vehicle steering apparatus. Various changes can be made.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus as a vehicle steering apparatus according to an embodiment of the present invention.
FIGS. 2A and 2B are schematic cross-sectional views of a main part of a vehicle steering system according to another embodiment of the present invention.
FIG. 3 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 4 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 5 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 6 is a schematic diagram of a main part of a control system of a vehicle steering system according to still another embodiment of the present invention.
FIG. 7 is a flowchart showing a flow of fail determination in the embodiment of FIG.
[Explanation of symbols]
1 Electric power steering device (vehicle steering device)
2 Steering member 6 Rack shaft (steering shaft)
13 Control unit (ECU)
15, 16 Driver 17, 18 Electric motor 19, 20 Motion conversion mechanism 21 Rack housing 22, 23 Stator 24, 25 Bearing 26, 27 Rotor 28, 29 Ball nut (rotary cylinder)
30 Ball 31 Elastic member 32 Rotor unit (common rotor)
33 (common) stator 35 (common) resolver (rotor rotation angle detecting means)
41, 42 Resolver (rotor rotation angle detection means)
131, 132 Control unit (ECU; means for determining abnormality)

Claims (5)

In a vehicle steering apparatus comprising a plurality of motors for driving a steering shaft extending in the left-right direction of the vehicle,
A plurality of motion converting mechanism for said plurality of motors enclose take each opposed and steering shaft in the axial direction of the steering shaft concentrically, converts each rotation of the motor rotor in the axial direction movement of the steering shaft Each of the motion conversion mechanisms includes a rotating cylinder that can rotate integrally with a rotor of a corresponding motor and surrounds the periphery of the steering shaft, and an elastic member is interposed between adjacent rotating cylinders. .   The vehicle steering apparatus according to claim 1, wherein the plurality of motors include one of a common stator and a common rotor. 3. The vehicle steering apparatus according to claim 1, wherein the plurality of motors include a common rotor rotation angle detection unit and are driven based on a detection signal of the rotor rotation angle detection unit. 3. The rotor rotation angle detecting means according to claim 1 or 2, wherein each of the plurality of motors includes a rotor rotation angle detecting means, and an abnormality of the rotor rotation angle detecting means or the motor is determined based on comparison of detection signals of the rotor rotation angle detecting means of the plurality of motors. The vehicle steering apparatus further comprising means for performing the operation. In a vehicle steering apparatus comprising a plurality of motors for driving a steering shaft extending in the left-right direction of the vehicle,
The plurality of motors face each other in the axial direction of the steering shaft and concentrically surround the steering shaft, and each of the plurality of motors includes a rotor rotation angle detection unit,
Based on the comparison of the detection signals of the rotor rotation angle detection means of a plurality of motors, the rotor rotation angle detection means or means for determining abnormality of the motor,
The plurality of motors are two motors,
The rotor rotation angle detection means or the means for determining whether the motor is abnormal is a means for calculating a difference between detection signals of the rotor rotation angle detection means included in each motor, and a first for comparing the calculated difference with a first threshold value. The comparison means, the second comparison means for comparing the calculated difference with a second threshold value greater than the first threshold value, and determining abnormality of the rotor rotation angle detection means based on the comparison result by the first comparison means A vehicle steering apparatus comprising: an abnormality determination unit that determines an abnormality of the motor based on a comparison result by the second comparison unit.

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