JP4487676B2 - Electric power steering device with variable transmission ratio mechanism - Google Patents

Description

  The present invention relates to an electric power steering apparatus provided with a transmission ratio variable mechanism that variably controls a ratio of a turning angle of a steered wheel to a steering angle of a steering wheel.

  As a transmission column variable mechanism that variably controls the ratio of the turning angle of the steered wheels with respect to the steering angle of the steering wheel, for example, the one described in Patent Document 1 is known.

   The thing of patent document 1 has the advantage which can mount | wear with a transmission ratio variable mechanism, without changing the structure by the side of a steering gear. On the other hand, in order to allow rotation of the motor itself while supplying an electric signal to the motor because the motor itself built in the housing of the variable transmission ratio mechanism must be rotated together with the steering shaft as the steering wheel rotates. Spiral cable is required.

For this reason, development of an electric power steering apparatus in which a transmission ratio variable mechanism is integrated into a steering gear box is underway.
Japanese Patent Laying-Open No. 2003-237590 (paragraphs 0015 to 0017, FIG. 2)

  By the way, as described in Patent Document 1, the transmission ratio variable mechanism transmits the rotational torque from the steering wheel to the output side via the wave gear mechanism. Sound is generated at the backlash. Therefore, in order to eliminate the generation of sound and enhance the durability, it is necessary to eliminate the backlash by press fitting.

  However, with the press-fit structure, there is a technical limitation that the press-fit load cannot be suppressed to a certain range unless the accuracy of a single product is increased. As a practical matter, the accuracy is naturally limited. It must be large.

  For this type of electric power steering device, it is desirable to assemble and assemble the transmission ratio variable mechanism and the torque sensor, respectively. However, if the press-fit load is large, such an assembly cannot be performed, and the transmission ratio is unavoidably changed to the torque sensor. A method of assembling the torque sensor incorporating the variable transmission ratio mechanism to the steering gear box after sequentially assembling the parts constituting the mechanism and integrating them together is unavoidable. Therefore, even if a characteristic abnormality or the like of the variable transmission ratio mechanism is discovered after it is assembled to the steering gear box, it is difficult to disassemble, and there is a possibility that a problem that the torque sensor must be discarded together with the variable transmission ratio mechanism may occur. .

  The present invention has been made to solve the above-described conventional problems, and provides an electric power steering apparatus including a transmission ratio variable mechanism that can reduce the press-fitting load and enables assembly in an assembly. Is.

In order to solve the above-mentioned problem, the constitutional feature of the invention according to claim 1 is that the transmission ratio variable mechanism assembled in the steering gear box, which is an electric power steering apparatus provided with the transmission ratio variable mechanism, and this transmission A sensor mechanism assembled to a variable ratio mechanism, the sensor mechanism being rotatably supported by the sensor housing, an input shaft that is rotatably supported by the sensor housing, and that transmits rotation of a steering wheel. An intermediate shaft supported and connected to the input shaft via a torsion bar, and a sensor unit for detecting a steering torque applied to the steering wheel based on relative rotation between the input shaft and the intermediate shaft, The transmission ratio variable mechanism includes a transmission ratio variable housing and a transmission ratio variable housing. An output shaft supported in a possible manner, a reduction gear housed in the transmission ratio variable housing and transmitting the rotation of the intermediate shaft to the output shaft, and an output shaft housed in the transmission ratio variable housing and via the reduction gear And a motor that changes the ratio of the turning angle of the steered wheels to the steering angle of the steering wheel, and the central portion of the rotation transmission engaging member that constitutes the reduction gear of the transmission ratio variable mechanism A cylindrical portion is provided, a through hole is formed in the central portion of the cylindrical portion, serrations are formed on the inner periphery of the through hole, and a plurality of the cylindrical portions are arranged on the circumference from the tip side. When the sensor mechanism is assembled to the transmission ratio variable mechanism, the slit is formed and an elastic engagement portion is formed so that the tip of the cylindrical portion is squeezed radially inward. , said Rolling transmitting engagement member is that it is configured to selector Shon engages the intermediate shaft of the sensor mechanism.

Further, the structural feature of the invention according to claim 2 is that, in claim 1, the transmission ratio variable mechanism is assembled, and a dummy shaft is arranged in place of the intermediate shaft, so that the transmission ratio variable mechanism alone It is configured to be able to perform a performance test.

Further, the structural feature of the invention according to claim 3 is that, in claim 1 or claim 2, the output shaft is a pinion shaft, and the steering gear box is a rack shaft that meshes with the pinion shaft. A ball screw mechanism including a ball screw nut screwed to the rack shaft, and an assisting electric motor that drives the ball screw mechanism to move the rack shaft in the axial direction are provided.

According to the invention of claim 1 constructed as described above, when assembling the sensor mechanism to the transmission ratio variable mechanism, no gap engagement with a relatively small press-fitting load of the intermediate shaft to the rotation transmitting engaging member of the reduction gear Since they are combined, they can be easily assembled without applying an excessive force to the torsion bar, and the two can be connected without backlash, so that the generation of sound can be prevented and the durability can be improved.

According to the invention according to claim 2 configured as described above, since the transmission ratio variable mechanism is assembled, there is an effect that a performance test can be performed alone before being assembled to the steering gear box.

According to the invention according to claim 3 configured as described above, there is an effect that the transmission ratio variable function can be easily applied to the rack assist type rack and pinion type electric power steering apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the electric power steering apparatus 10 of the present embodiment is mainly configured by a steering gear box 11, a transmission ratio variable mechanism 12, and a sensor mechanism 13.

  The rotation of the steering wheel 15 is transmitted to the input shaft 14 of the electric power steering apparatus 10 via the steering shaft 16. A rack shaft 17 is meshed with the output shaft of the electric power steering apparatus 10 in the steering gear box 11. One end of a tie rod 18 is connected to each end of the rack shaft 17, and the other end of each tie rod 18 is connected to a steered wheel 19 via a knuckle arm.

  The steering angle of the steering wheel 15 is detected by a steering angle sensor 85 provided on the steering shaft 16, and the turning angle of the steered wheels 19 is a rotation angle built in an assist electric motor described later. It is to be detected by a sensor. The steering angle of the steering wheel 15 and the turning angle of the steered wheel 19 are input to the ECU 86. The ECU 86 also receives a vehicle speed output from a vehicle speed sensor 87 that detects the vehicle speed. The ECU 86 outputs a control signal for controlling the transmission ratio variable mechanism 12 based on the steering angle, the turning angle, and the vehicle speed.

  2 and 3, the steering gear box 11 has a first gear housing 21, a motor housing 22, and a second gear housing 23 that are coupled to each other, and a pinion shaft 24 is provided in the first gear housing 21. The bearings 25 and 26 are rotatably supported. The pinion shaft 24 constitutes an output shaft in the rack and pinion type steering. A rack shaft 17 is inserted into the first gear housing 21, the motor housing 22, and the second gear housing 23 so as to be slidable in a direction perpendicular to the axis of the pinion shaft 24. Left and right steered wheels 19 are connected to both ends of the rack shaft 17 via tie rods 18. A rack tooth 28 is formed on the rack shaft 17, and a pinion tooth 29 formed on the pinion shaft 24 is meshed with the rack tooth 28.

  In the motor housing 22, a stator 31 constituting an assisting electric motor 30 and a cylindrical motor shaft 32 are accommodated. The stator 31 is wound and is fitted to the inner periphery of the motor housing 22. A permanent magnet 38 is attached to the outer periphery of the motor shaft 32 corresponding to the stator 31. The motor shaft 32 is rotatably supported by the motor housing 22 via bearings 33 and 34, and is loosely coaxially fitted around the rack shaft 17 inside the stator 31. The rotation angle of the motor shaft 32, that is, the turning angle of the steered wheels 19 is detected by a rotation angle sensor 35 formed of a motor resolver provided on the outer peripheral side of the motor shaft 32.

  A ball screw nut 36 is coaxially fitted in the motor shaft 32, and a spiral ball screw groove is provided on the inner peripheral surface of the ball screw nut 36. Further, a spiral ball screw groove is provided in a predetermined range in the axial direction on the outer peripheral surface of the rack shaft 17, and a large number of balls are accommodated between the ball screw grooves in a rollable manner. With the ball screw mechanism 37 having such a configuration, the rotational torque of the forward / reverse rotation of the motor shaft 32 is converted into the axial reciprocation of the rack shaft 17.

  The transmission ratio variable mechanism 12 has a function of making the ratio (transmission ratio) of the turning angle of the steered wheels 19 to the steering angle of the steering wheel 15 variable according to the vehicle speed, for example.

  The transmission ratio variable mechanism 12 includes a cylindrical transmission ratio variable housing 41. The housing 41 is fitted into the opening of the first gear housing 21 and is integrally coupled by a bolt 42. One end of the housing 41 fitted to the first gear housing 21 is fitted with the bearing 26 for supporting one end side (an adapter portion described later) of the pinion shaft 24, and the pinion shaft 24 has an assembly transmission ratio. A part of the variable mechanism 12 is configured. The pinion shaft 24 includes a pinion shaft portion 43 that meshes with the rack shaft 17 and an adapter portion 44 in which a large-diameter storage recess 44a that stores a reduction gear 45 including a wave gear mechanism described later is formed. The adapter portion 44 is integrally connected to the outer periphery of one end of the pinion shaft portion 43 by serration coupling by press fitting.

  As described above, since the pinion shaft 24 is divided into the pinion shaft portion 43 and the adapter portion 44, there is no interference (adapter portion 44) when finishing the pinion teeth 29 with the carbide hob cutter. Since the hard hob finishing can be easily performed and there is no processing restriction, the large-diameter storage recess 44a can be provided as close to the pinion teeth 29 as possible. Thereby, the axial length of the pinion shaft 24 can be shortened, and vehicle mounting property can be improved.

  In the housing 41, an adapter portion 44 of the pinion shaft 24, a speed reducer (differential mechanism) 45, a motor (DC brushless motor) 46, and a lock mechanism 47 are accommodated. For example, the speed reducer 45 includes a wave gear mechanism, and includes a driven gear 49, a stator gear 50, a wave generator 51, a flexible gear 52, and a rotation transmission engagement member 53, as will be described in detail later. ing.

  A driven gear 49, a stator gear 50, and a rotation transmission engaging member 53 are housed in the housing recess 44a formed in the adapter portion 44 in order from the opening end side. The driven gear 49 is press-fitted and coupled to the storage recess 44a, and the stator gear 50 and the rotation transmission engagement member 53 are coupled in the rotation direction so as to be rotatable within the storage recess 44a. As shown in detail in FIG. 4, the rotation transmission engagement member 53 is formed in a disk shape as a whole, has a cylindrical portion 54 extending toward the pinion shaft 24, and has a through hole 55 in the center. ing. A serration engaging portion 53a is formed on the inner peripheral surface of the through hole 55, and the serration engaging portion 53a is loosely fitted to a serration engaging portion formed on the intermediate shaft, as will be described later. The cylindrical portion 54 is formed with a plurality of slits 54a on the circumference to reduce the rigidity in the radial direction, and is elastically deformed so that the tip is squeezed radially inward to form the elastic engagement portion 53b. ing.

  Gears having different numbers of teeth (the number of teeth of the driven gear 49 <the number of teeth of the stator gear 50) are formed on the inner peripheral surfaces of the driven gear 49 and the stator gear 50, respectively. Inside the driven gear 49 and the stator gear 50, there are provided flexible gears 52 that simultaneously mesh with the respective gears. That is, the teeth formed on the inside of the driven gear 49 and the stator gear 50 mesh with the teeth formed on the outside of the flexible gear 52 (the number of teeth is the same as the number of teeth of the driven gear 49). The inner side of the flexible gear 52 is fitted on the outer ring of the wave generator 51.

  A case 57 of the motor 46 is fixed to the housing 41. The motor 46 has a motor shaft 58, and the motor shaft 58 is rotatably supported by the case 57 via bearings 59 and 60 and is connected to the cam of the wave generator 51. An intermediate shaft 75 that constitutes a part of the sensor mechanism 13 described later is rotatably inserted into the motor shaft 58. A serration engagement portion 75 a that loosely engages with the serration engagement portion 53 a of the rotation transmission engagement member 53 is formed on the outer periphery of the distal end portion of the intermediate shaft 75. The intermediate shaft 75 is engaged with the serration engagement portion 53a of the rotation transmission engagement member 53, and can be engaged with the elastic engagement portion 53b without play with a relatively small press-fit load.

  In this configuration, as shown in FIG. 2, when the motor shaft 58 of the motor 46 rotates, the cam of the wave generating device 51 rotates, and the flexible gear 52 deforms into an elliptical shape in the stator gear 50, thereby driving the coaxial driven gear 49. Rotate. That is, since the number of teeth of the driven gear 49 is smaller than the number of teeth of the stator gear 50, when the wave generating device 51 makes one rotation, the driven gear 49 rotates by a difference in the number of teeth in the direction opposite to the rotation direction of the wave generating device 51 ( That is, the actuator operating angle = the rotation angle of the motor 46 × the reduction ratio (reduction ratio = the difference in the number of teeth / the number of teeth in the driven gear 49) On the other hand, when the stator gear 50 is rotated by the rotation of the steering wheel 15, the actuator operating angle is added. It is transmitted to the pinion shaft 24.

  The lock mechanism 47 fixes (locks) the motor shaft 58 to the transmission ratio variable housing 41 when the power is turned off or the system is defective. Thus, the rotation of the steering wheel 15 is reliably transmitted to the steered wheels 19 even in the locked state, but since it is a known technique, the description thereof is omitted.

  As an example, the sensor mechanism 13 is configured by a twin resolver type sensor as described in JP-A-2004-117328.

  The sensor mechanism 13 includes a sensor housing 71. The input shaft 14 is rotatably supported by a bearing 72 provided at the front end of the housing 71, and the intermediate shaft 75 is concentric with the input shaft 14 at a bearing 74 provided at the rear end of the housing 71. It is rotatably supported. The input shaft 14 and the intermediate shaft 75 are connected via a torsion bar 76 so as to be relatively rotatable by a predetermined amount. The intermediate shaft 75 passes through the motor shaft 58 of the transmission ratio variable mechanism 12 when assembled, and is serrated to the rotation transmission engagement member 53 of the speed reducer 45.

  A coil 77 is housed in the housing 71. The coil 77 is composed of a stator 78, a substrate 79 fixed to the stator 78, and a lead wire 80 electrically connected to the substrate 79. Yes. The stator 78 has a plurality of windings, has an annular shape extending in the circumferential direction surrounding the torsion bar 76, and is fixed to the inner periphery of the housing 71. A first rotor 81 and a second rotor 82 are housed inside the coil 77, and the first rotor 81 has a plurality of windings and has an annular shape extending in the circumferential direction surrounding the torsion bar 76. The input shaft 14 is fixed. The second rotor 82 also has a plurality of windings, has an annular shape extending in the circumferential direction surrounding the torsion bar 76, and is fixed to the intermediate shaft 75. The stator (winding) 78 is electrically separated into a portion facing the first rotor 81 and a portion facing the second rotor 82, and an output is obtained from each of these two portions. .

  In the sensor mechanism 13 configured as described above, when a current is supplied from the microcomputer to the input winding of the stator 78 via the substrate 79, an induced current flows through the output winding of the winding. Then, when torque is transmitted to the input shaft 14 by operating the steering wheel, the torsion bar 76 is twisted to cause relative rotation between the input shaft 14 and the intermediate shaft 75. Thereby, the first rotor 81 and the second rotor 82 are rotationally displaced with respect to the stator 78, respectively, and an output difference from the two portions of the stator 78 is input to the microcomputer via the substrate 79 as a steering torque signal.

  Next, a procedure for assembling the electric power steering apparatus 10 having the above-described configuration will be described.

  The transmission ratio variable mechanism 12 and the sensor mechanism 13 are assembled together. The assembly assembled transmission ratio variable mechanism 12 includes a pinion shaft 24 supported by the transmission ratio variable housing 41, and the assembly assembled sensor mechanism 13 includes an intermediate shaft 75 supported by the sensor housing 71. Have

  When performing a performance test of the transmission ratio variable mechanism 12 in such an assembly state, a dummy shaft is inserted into the motor shaft 58 instead of the intermediate shaft 75 and is serrated to the rotation transmission engagement member 53. As a result, before the transmission ratio variable mechanism 12 is assembled to the steering gear box 11, a performance test can be performed as a single unit with the dummy shaft as the input side and the pinion shaft 24 as the output side.

  In assembling the electric power steering apparatus 10, first, the transmission ratio variable mechanism 12 is assembled to the steering gear box 11. That is, with the pinion shaft 24 engaged with the rack shaft 17, the shaft end of the pinion shaft 24 is fitted to the bearing 25 while the variable transmission ratio housing 41 is fitted to the opening of the first gear housing 21. Thereafter, the transmission ratio variable housing 41 is coupled to the first gear housing 21 by the bolt 42, and a nut 90 (see FIG. 2) is fastened to the shaft end of the pinion shaft 24 to position the pinion shaft 24 at a predetermined position. .

  Next, the sensor mechanism 13 is assembled to the transmission ratio variable mechanism 12 assembled to the steering gear box 11. That is, while the intermediate shaft 75 is inserted into the motor shaft 58 and the serration engagement portion 75a of the intermediate shaft 75 is engaged with the serration engagement portion 53a formed on the rotation transmission engagement member 53 of the speed reducer 45, the sensor The housing 71 is pushed into a position where the end surface of the housing 71 comes into contact with the end surface of the variable transmission ratio housing 41. At this time, the serration engaging portion 75 a of the intermediate shaft 75 is configured to loosely fit with the serration engaging portion 53 a of the rotation transmission engaging member 53, and the elastic engagement portion 53 b of the rotation transmission engaging member 53. It is designed to engage with a relatively small press-fit load without a gap. Therefore, the sensor mechanism 13 can be easily assembled without applying an excessive force to the torsion bar 76. Thereafter, the sensor housing 71 is fixed to the transmission ratio variable housing 41 with bolts (not shown), and the assembly of the electric power steering apparatus 10 is completed.

  According to the electric power steering apparatus 10 having the above-described configuration, when the driver steers the steering wheel 15, the steering torque applied to the steering wheel 15 is detected by the sensor mechanism 13, and the assist is performed according to the detected steering torque. The electric motor 30 is controlled.

  Further, according to the electric power steering apparatus 10 having the above-described configuration, when the driver steers the steering wheel 15 in a state where the lock mechanism 47 is unlocked, the steering angle of the steering wheel 15 is detected by the steering angle sensor 85. Is done. The ECU 86 inputs the steering angle from the rudder angle sensor 85 and inputs the vehicle speed from the vehicle speed sensor 87. Then, the ECU 86 calculates the target rudder angle based on the vehicle speed and the steering angle. A control signal for controlling the motor 46 is output from the ECU 86 based on the target steering angle.

  The control signal output from the ECU 86 is sent to the motor 46 of the transmission ratio variable mechanism 12, and the motor 46 is rotationally driven based on this control signal. When the motor 46 is rotated, the cam of the wave generator 51 is rotated via the motor shaft 58, and the flexible gear 52 is rotated. The flexible gear 52 rotates in the stator gear 50 in a state of being deformed into an ellipse, and rotates the driven gear 49 on the same axis. At this time, since the number of teeth of the driven gear 49 is smaller than the number of teeth of the stator gear 50, when the wave generating device 51 makes one rotation, the driven gear 49 rotates in the direction opposite to the rotation direction of the wave generating device 51 by the difference in the number of teeth. .

  The rotation of the driven gear 49 is transmitted to the pinion shaft 24 and causes the rack shaft 17 to move. Thereby, the ratio of the steering angle of the steering wheel 15 and the turning angle of the steered wheels 19 can be changed. Then, the turning angle of the steered wheel 19 detected by the rotation angle sensor 35 is fed back to the ECU 86 so that the steered angle corresponding to the target steered angle can be reliably given to the steered wheel 19.

  In the above embodiment, the reduction gear 45 of the variable transmission ratio mechanism 12 has been described by taking a reduction gear made of a wave gear mechanism as an example. However, the reduction gear 45 is not limited to this, for example, a sun gear, A planetary gear mechanism including an internal gear and a planetary gear may be used.

  In the above embodiment, the sensor mechanism 13 has been described as a twin resolver type. However, the sensor mechanism 13 is not limited to this, and for example, in addition to the steering wheel 15 such as a variable inductance torque sensor. Any system having a function of detecting the steering torque generated can be applied.

1 is an overall configuration diagram of a steering device showing an embodiment of the present invention. It is sectional drawing of the electric power steering device provided with the transmission ratio variable mechanism which shows embodiment of this invention. It is sectional drawing which shows a steering gear box. It is sectional drawing which shows the detail of the rotation transmission engagement member in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 11 ... Steering gear box, 12 ... Transmission ratio variable mechanism, 13 ... Sensor mechanism, 14 ... Input shaft, 15 ... Steering wheel, 17 ... Rack shaft, 19 ... Steering wheel, 24 ... Pinion shaft ( (Output shaft), 30 ... electric motor for assist, 37 ... ball screw mechanism, 41 ... variable transmission ratio housing, 45 ... speed reducer, 46 ... motor, 53 ... rotation transmission engaging member, 53a ... serration engaging portion, 53b ... Elastic engagement portion, 58... Motor shaft, 71... Sensor housing, 75.

Claims (3)

An electric power steering apparatus having a transmission ratio variable mechanism, comprising: a transmission ratio variable mechanism assembled to a steering gear box; and a sensor mechanism assembled to the transmission ratio variable mechanism, wherein the sensor mechanism includes a sensor housing, An input shaft rotatably supported by the sensor housing and transmitting rotation of a steering wheel; an intermediate shaft rotatably supported by the sensor housing and connected to the input shaft via a torsion bar; and the input shafts And a sensor unit that detects a steering torque applied to the steering wheel based on relative rotation between the intermediate shaft and the intermediate shaft, and the transmission ratio variable mechanism is rotatable to the transmission ratio variable housing and the transmission ratio variable housing. In the supported output shaft and the transmission ratio variable housing A reduction gear that transmits the rotation of the intermediate shaft to the output shaft, and a rotation of the steered wheels with respect to the steering angle of the steering wheel that is housed in the transmission ratio variable housing and transmits the rotation to the output shaft via the reduction gear. And a motor that changes the ratio of the turning angle, and a cylindrical portion is provided at the center of the rotation transmission engaging member that constitutes the speed reducer of the transmission ratio variable mechanism. A through hole is formed, serrations are formed on the inner periphery of the through hole, a plurality of slits are formed on the cylindrical portion from the distal end side to the circumference, and the distal end of the cylindrical portion is in the radial direction. elastic engagement portion which is molded as squeezed inwardly are formed, when the sensor mechanism is assembled to the transmission ratio variable mechanism, selector Shon the intermediate shaft of the rotation transmitting engaging member sensor mechanism Engage An electric power steering apparatus having a variable transmission ratio mechanism, characterized in that it is configured. 2. The transmission ratio variable mechanism according to claim 1, wherein the transmission ratio variable mechanism is an assembly, and a dummy shaft is disposed in place of the intermediate shaft so that a performance test can be performed by the transmission ratio variable mechanism alone. Electric power steering device with 3. The ball screw mechanism according to claim 1 , wherein the output shaft includes a pinion shaft, and the steering gear box includes a rack shaft that meshes with the pinion shaft, and a ball screw nut that is screwed into the rack shaft. An electric power steering device provided with a transmission ratio variable mechanism provided with an assisting electric motor that drives the ball screw mechanism to move the rack shaft in the axial direction .

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