JP2006036142A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect at an early stage occurrence of slip in a rotational force transmission system from an electric motor to a rack shaft in an electric power steering device.
In an electric power steering apparatus 10 for converting the rotation of an electric motor 20 into a linear stroke of a rack shaft 14 via a power transmission mechanism and steering a wheel connected to the rack shaft 14, the number of rotations of the electric motor 20 is increased. When the movement stroke movement displacement amount of the rack shaft 14 corresponding to the accumulated rotation number is calculated, and the movement stroke movement displacement amount of the rack shaft 14 exceeds the specified maximum stroke amount of the rack shaft 14, A motor slip detecting means 60 for estimating the occurrence of slipping and slipping in the rotational force transmission system from the electric motor 20 to the rack shaft.
[Selection] Figure 3

Description

  The present invention relates to an electric power steering apparatus.

As described in Patent Document 1, the electric power steering device detects the steering torque of the steering system with a steering torque sensor, sets a target current based on the detected steering torque, and sets the target current and the current that actually flows through the electric motor. The electric motor is driven and controlled by a PWM (Pulse Width Modulation) signal obtained by performing PI (proportional / integral) compensation on the deviation, and the rack shaft is linearly stroked to exert a steering assist force on the wheels connected to the rack shaft.
JP-A-6-8839

  In the conventional electric power steering device, even if slip occurs in the rotational force transmission system from the electric motor to the rack shaft, the occurrence of the slip cannot be detected at an early stage, and the steering assist control may become unstable. The slip generated in the rotational transmission system of the electric motor is not caused by damage to the belt transmission mechanism or the ball screw device that converts the rotation of the electric motor into a linear stroke of the rack shaft, or loosening of the fixed connection portion of the transmission mechanism. There are regular idling.

  An object of the present invention is to early detect the occurrence of slipping in a rotational force transmission system from an electric motor to a rack shaft in an electric power steering apparatus.

  The invention according to claim 1 is an electric power steering device that converts the rotation of the electric motor into a linear stroke of the rack shaft by a power transmission mechanism, and steers the wheel connected to the rack shaft. When the movement stroke displacement amount of the rack shaft corresponding to this accumulated rotational speed is calculated and the movement stroke displacement amount of the rack shaft exceeds the predetermined maximum stroke displacement amount of the rack shaft, the electric motor changes to the rack shaft. A motor slip detecting means for estimating that slip has occurred in the rotational force transmission system is provided.

  According to a second aspect of the present invention, in the first aspect of the invention, the motor slip detection means further includes a control means for controlling the stop of the electric motor when the occurrence of slippage in the rotational force transmission system of the electric motor is detected. Is.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the motor slip detection means further includes an alarm output means for outputting an alarm when the occurrence of slippage in the rotational force transmission system of the electric motor is detected. It is a thing.

  According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, the rotational force of the driving pulley fixed to the rotating shaft of the electric motor is further changed to a driven pulley connected to the driving pulley by a winding body. The drive shaft is connected to the rack shaft through a power transmission mechanism including the power transmission mechanism.

  According to a fifth aspect of the present invention, there is provided the power transmission mechanism according to any one of the first to third aspects, further comprising a driven gear that meshes the rotational force of the drive gear fixed to the rotary shaft of the electric motor with the drive gear. Via the rack shaft.

(Claim 1)
(a) When the rotation speed of the electric motor at the forward rotation is a positive rotation speed, the rotation speed at the reverse rotation is a negative rotation speed, and the rotation speed of the electric motor is integrated, the positive integrated rotation quantity is, for example, left Corresponding to the left steering amount accumulated in the steered direction, the negative integrated rotation amount corresponds to the right steering amount accumulated in the right steered direction.

  Then, the rack corresponding to the accumulated rotational speed is obtained by multiplying the accumulated rotational speed of the electric motor by the linear stroke conversion constant (the stroke movement displacement amount of the rack shaft when the electric motor rotates once) by the power transmission mechanism of the rack shaft. The movement stroke displacement amount of the shaft, in other words, the movement stroke displacement amount of the rack shaft accumulated in the left steering direction or the right steering direction can be calculated.

  Therefore, when the displacement of the movement stroke exceeds the predetermined maximum stroke displacement of the rack shaft, at least a part of the rotation of the electric motor is actually not properly transmitted to the rack shaft. Judgment can be made to presume that any of the drive transmission systems from the electric motor to the rack shaft is idling or slipping, and the occurrence of slippage in the rotational force transmission system from the electric motor to the rack shaft can be easily detected at an early stage. .

(Claim 2)
(b) When the motor slip detection means detects the occurrence of slip in the torque transmission system of the electric motor, the current control calculation means instantaneously sets the duty ratio of the PWM signal to zero so that the steering assist in an unstable state Control can be released immediately.

(Claim 3)
(c) When the motor slip detection means detects the occurrence of slip in the rotational force transmission system of the electric motor, the alarm output means outputs an alarm and can immediately notify the user of the abnormality in the steering assist control.

(Claim 4)
(d) When the power transmission mechanism from the electric motor to the rack shaft is composed of a wound body wound around the drive pulley and the driven pulley, the slip of the above (a) caused by cutting of the wound body can be detected.

(Claim 5)
(e) When the power transmission mechanism from the electric motor to the rack shaft is composed of a gear train of a drive gear and a driven gear, it is possible to detect the slip of the above (a) caused by a gear tooth breakage or the like.

  FIG. 1 is a front view showing an electric power steering apparatus, FIG. 2 is a cross-sectional view showing a main part of the electric power steering apparatus, FIG. 3 is a block diagram showing a control system of the electric power steering apparatus, and FIG. It is a flowchart shown.

  As shown in FIG. 1, the electric power steering apparatus 10 includes a first gear housing 11A and a second gear housing 11B in which the gear housing 11 is divided, and a steering input is input to the gear housing 11 (first gear housing 11A). The shaft 12 is supported, an output shaft (not shown) is connected to the input shaft 12 via a torsion bar 13, a pinion (not shown) is provided on the output shaft, and the rack shaft 14 meshing with the pinion is connected to the gear housing 11. It is supported so that it can move linearly in the left-right direction. A steering torque sensor 41 is provided between the input shaft 12 and the output shaft. The steering torque sensor detects the steering torque based on the relative rotational displacement generated between the input shaft 12 and the output shaft due to the elastic torsional deformation of the torsion bar caused by the steering torque applied to the steering wheel, and detects the steering torque signal Ts. Is output.

  The electric power steering apparatus 10 has both end portions of the rack shaft 14 projecting from both sides of the gear housing 11 (first gear housing 11A, second gear housing 11B), and tie rods 15A, 15B are connected to the end portions of the rack shaft 14, The left and right wheels can be steered via tie rods 15A and 15B that are linked to the 14 linear movements.

  As shown in FIG. 2, the electric power steering apparatus 10 fixes the electric motor 20 to a holder 22 with mounting bolts 21 (not shown), and the holder 22 is detachably attached to the first gear housing 11 </ b> A with mounting bolts 23. . The holder 22 attached to the first gear housing 11A and inserted into the first gear housing 11A has a certain gap between the inner periphery of the gear housings 11A and 11B, and is a holder for the first gear housing 11A. 22 is allowed to swing, and the tension of the belt 37 wound around the drive pulley 24 and the driven pulley 36 supported on the holder 22 as described later can be adjusted.

  At this time, the holder 22 supports the central shaft 25 of the drive pulley 24, and the joint 26A at the shaft end of the rotating shaft 20A of the electric motor 20 and the joint 26B at the shaft end of the central shaft 25 are arranged at a plurality of positions in the circumferential direction. The intermediate joints 26C made of rubber or the like are sandwiched between the teeth provided on the two sides, and are engaged with each other from the axial direction. The drive pulley 24 is supported by the holder 22 at both ends of the central shaft 25 by bearings 27 and 28. Reference numeral 29 denotes a retaining ring for fixing the outer ring of the bearing 28.

  The electric power steering apparatus 10 includes a ball screw 30 on the rack shaft 14, a ball nut 32 that meshes with the ball screw 30 via a ball 31, and a bearing 33 supported by the gear housing 11 (first gear housing 11 </ b> A). Thus, the ball nut 32 is rotatably supported. Reference numeral 34 denotes an outer ring fixing nut of the bearing 33. A driven pulley 36 is fixed to the outer periphery of the ball nut 32 by a lock nut 35.

  The electric power steering apparatus 10 wraps a belt 37 around a drive pulley 24 on the electric motor 20 side and a driven pulley 36 on the ball nut 32 side, and rotates the electric motor 20 to drive pulley 24, belt 37, driven pulley 36. Then, it is transmitted to the ball nut 32 and converted into a linear stroke of the rack shaft 14, and the rack shaft 14 is linearly moved. Thereby, the electric motor 20 provides a steering assist force to the steering system.

  The electric power steering apparatus 10 passes the rack shaft 14 supported by the first gear housing 11A through the second gear housing 11B, covers the holder 22 attached to the first gear housing 11A with the second gear housing 11B, The first gear housing 11 </ b> A and the second gear housing 11 </ b> B are fastened with a plurality of fastening bolts 16. At this time, as shown in FIG. 2, the first gear housing 11A and the second gear housing 11B are driven by the plurality of cylindrical knock pins 16A so that both end portions of the knock pins 16A are driven and aligned. The fastening bolt 16 inserted through 16A is screwed and fastened. Some fastening bolts 16 are screwed to the first gear housing 11A through the knock pins 16A, and other fastening bolts 16 are screwed to the second gear housing 11B through the knock pins 16A.

  The electric power steering apparatus 10 has the following configuration in order to reduce the swing of the rack shaft 14 supported by the gear housings 11A and 11B.

  In the second gear housing 11 </ b> B, a portion facing the ball nut 32 supported by the first gear housing 11 </ b> A is a bush support portion 17, and the bush 40 is bridged between the ball nut 32 and the bush support portion 17. The bush 40 is press-fitted into the inner peripheral portion on the tip end side of the ball nut 32 and is fixedly provided. The bush 40 is linearly slid on the rack shaft 14 while being rotatably supported by the inner peripheral portion of the bush support portion 17. Support as possible.

  The bush 40 has a part in the axial direction of the outer periphery of a cylindrical body made of metal or the like as a sliding part with the bush support part 17, and an entire inner periphery as a sliding part with the rack shaft 14. The sliding portion is obtained by providing a lubrication coating layer such as an oil-containing polyacetal resin or a tetrafluoroethylene resin on the surface of the cylindrical body by coating or the like.

  The electric power steering apparatus 10 has the following control means 50 for the electric motor 20 (FIG. 3).

  The control means 50 includes a steering torque sensor 41 and a vehicle speed sensor 42 as incidental. As described above, the steering torque sensor 41 detects the steering torque of the steering system and outputs the steering torque signal Ts to the control means 50. The vehicle speed sensor 42 detects the speed of the vehicle and outputs a vehicle speed signal Vs to the control means 50.

  The control means 50 is based on a microprocessor and has various arithmetic processing means, signal generation means, memory, etc., and performs P (proportional control) and I (integral control) based on the steering torque signal Ts and the vehicle speed signal Vs. The generated drive control signal V0 (PWM signal) is generated, and thereby the motor drive means 43 is driven and controlled.

  The motor driving means 43 is constituted by a bridge circuit composed of switching elements such as four power FETs (field effect transistors) or IGBTs (insulated gate / bipolar transistors), for example, and outputs a motor voltage Vm based on the drive control signal V0. Then, the electric motor 20 is driven. When the steering wheel is being steered in the clockwise direction, the electric motor 20 is rotated forward, for example, to apply a steering assist force to the steering system so that the front wheels face in the clockwise direction.

  The control unit 50 includes a current detection unit 44 incidentally. The current detection unit 44 detects the motor current Im actually flowing through the electric motor 20 and feeds back (negative feedback) the detection current signal Imo converted to digital corresponding to the motor current Im to the control unit 50.

  The control unit 50 includes a target current setting unit 51, a deviation calculation unit 52, and a current control calculation unit 53.

  The target current setting means 51 includes a memory such as a ROM (Read Only Memory), and is based on the steering torque signal Ts output from the steering torque sensor 41 and the vehicle speed signal Vs output from the steering torque signal Ts and the vehicle speed sensor 42. The target current signal Ims for the steering torque signal Ts using the vehicle speed signal Vs as a parameter is read from the target current signal Ims map stored in advance in the memory and output to the deviation calculating means 52.

  The deviation calculating means 52 calculates a deviation (Ims−Imo) between the target current signal Ims and the detected current signal Imo, and outputs a deviation signal ΔI to the current control calculating means 53.

  The current control calculation means 53 is a PWM corresponding to a polarity signal and a duty ratio to the motor drive means 43 of the electric motor 20 in accordance with the deviation signal ΔI between the target current signal Ims and the detected current signal Imo. A signal Vo is given.

  The current control calculation unit 53 includes a PI (proportional / integral) control unit 54 and a PWM signal generation unit 55.

  The PI control means 54 generates a proportional sensitivity KP for proportional control 54A, an integral element 54B for integrating control by generating an integral gain KI, and an addition for adding the output signals of the proportional element 54A and the integral element 54B. 54C is provided. The proportional element 54A and the integral element 54B are connected in parallel, the proportional element 54A is a proportional signal IP obtained by multiplying the deviation signal ΔI by the proportional sensitivity KP, and the integral element 54B is an integral obtained by subjecting the deviation signal ΔI to integration processing having an integral gain KI. The signal II is output to the adder 54C. The adder 54C adds the proportional signal IP and the integral signal II, and outputs the proportional / integral signal IPI (IP + II) to the PWM signal generating means 55.

  The PWM signal generation means 55 outputs a direction polarity signal corresponding to the direction and magnitude of the proportional / integral signal IPI and a PWM signal corresponding to the duty ratio to the motor drive means 43 as the drive control signal Vo. The motor driving means 43 drives the electric motor 20 with the motor driving voltage Vm.

Therefore, the control means 50 operates the electric power steering apparatus 10 as follows.
(1) When the steering torque detected by the steering torque sensor 41 is lower than a predetermined value, the steering assist force is unnecessary and the electric motor 20 is not driven.

  (2) Since the steering assist force is required when the steering torque detected by the steering torque sensor 41 exceeds a predetermined value, the electric motor 20 is driven. The rotational force of the electric motor 20 is transmitted to the ball nut 32 via the drive pulley 24, the belt 37, and the driven pulley 36, and becomes a steering assist force that causes the rack shaft 14 to linearly stroke via the ball screw 30.

  However, the electric power steering apparatus 10 is provided with the motor slip detection means 60 in the control means 50 in order to detect the occurrence of slip in the rotational force transmission system from the electric motor 20 to the rack shaft 14, and the motor slip detection means 60 is electrically driven. The rotation detection means 61 of the motor 20 and the alarm output means 62 are attached.

  Note that the slip of the electric motor 20 is caused by slippage between any connecting portions in the rotational force transmission system from the electric motor 20 to the rack shaft 14 or idling due to breakage of the mesh, for example, the center of the electric motor 20 and the drive pulley 24. Breakage or slip of the joint (26A to 26C) with the shaft 25, slip of the fitting portion between the drive pulley 24 and the central shaft 25, cutting or slip of the belt 37, slip of the joint of the ball nut 32 and the driven pulley 36, This is due to damage of the ball screw 30 or the like.

  The motor slip detection means 60 detects the occurrence of slip in the rotational force transmission system from the electric motor 20 to the rack shaft 14 as follows (FIG. 4).

(1) The rotational speed Σn of the electric motor 20 is integrated.
The rotation detection means 61 detects the rotation speed Nm of the electric motor 20 and outputs a detected rotation speed signal Nmo to the motor slip detection means 60. Based on the detected rotational speed signal Nmo, the motor slip detection means 60 sets the rotational speed at the forward rotation of the electric motor 20 to a positive rotational speed, sets the rotational speed at the reverse rotation to a negative rotational speed, and rotates the electric motor 20. The number is accumulated to obtain an accumulated rotational speed Σn. The positive accumulated rotational speed Σn corresponds to, for example, the left steering amount accumulated in the left steering direction, and the negative accumulated rotational speed Σn corresponds to the right steering amount accumulated in the right steering direction.

  (2) The movement stroke displacement amount Rs of the rack shaft 14 corresponding to the integrated rotational speed Σn of the electric motor 20 of (1) described above is calculated. The motor slip detection means 60 adds the linear stroke conversion constant (the stroke change length of the rack shaft 14 per one rotation of the electric motor 20) to the integrated rotational speed Σn of the electric motor 20 (the electric motor 20 Multiplying the reduction ratio of the power transmission path from to the ball nut 32 and the multiplication value of the lead of the ball screw 30), the movement stroke displacement amount Rs of the rack shaft 14 corresponding to the integrated rotational speed Σn, in other words, left The movement stroke displacement amount Rs of the rack shaft 14 accumulated in the turning direction or the right turning direction can be calculated.

  (3) When the movement stroke displacement amount Rs of the rack shaft 14 in the above (1) is compared with the specification maximum stroke Rmax (specified value) of the rack shaft 14, and the movement stroke displacement amount Rs exceeds the maximum use stroke Rmax, It is determined that some slippage or idling occurs in the rotational force transmission system from the electric motor 20.

  The motor slip detecting means 60 controls the PWM signal generating means 55 by outputting a motor stop control signal A to the PWM signal generating means 55 when detecting the occurrence of slipping and idling in the rotational force transmission system from the electric motor 20. The duty ratio D of the PWM signal Vo output from the PWM signal generating means 55 is set to zero. Thereby, useless driving of the electric motor 20 is controlled to stop. Further, irregular slip detection may be performed in the initial slip state of the rotational force transmission system. This is because the transmission system has not yet completely slipped and the engagement state is determined to be in an unstable connection state, and the duty ratio D of the PWM signal Vo output by the PWM signal generation means 55 is cut off. It may be reduced to zero.

  When the motor slip detection means 60 detects the occurrence of slippage in the rotational force transmission system from the electric motor 20, the motor slip detection means 60 outputs the alarm output signal B to the alarm output means 62 to control the alarm output means 62 to To output visual and auditory warnings.

According to the present embodiment, the following operational effects can be obtained.
(a) The movement stroke displacement amount Rs calculated by the motor slip detection means 60 exceeds the specified maximum stroke Rmax, which is a predetermined specified value of the rack shaft 14, because at least a part of the rotation from the electric motor 20 is actually a rack. This means that the electric motor 20 is slipping and idling, which means that it is not transmitted to the shaft 14, and it is easy to quickly generate slipping and idling of the rotational force transmission system from the electric motor 20 to the rack shaft 14. Can be detected.

  (b) When the motor slip detection means 60 detects the occurrence of slippage of the rotational force transmission system from the electric motor 20, the unstable steering assist control can be immediately canceled by controlling the electric motor 20 to stop.

  (c) When the motor slip detection means 60 detects the occurrence of slip in the rotational force transmission system of the electric motor 20, the alarm output means 62 outputs an alarm, and can immediately notify the user of the abnormality in the steering assist control.

  (d) When the power transmission mechanism from the electric motor 20 to the rack shaft 14 includes the belt 37 wound around the drive pulley 24 and the driven pulley 36, the slip of the above-mentioned (a) caused by cutting, loosening, etc. of the belt 37 is caused. It can be detected.

  (e) When the power transmission mechanism from the electric motor 20 to the rack shaft 14 is composed of a gear train of a drive gear and a driven gear, it is possible to detect the slip of the above (a) caused by a gear tooth breakage or the like.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. For example, a power transmission mechanism that transmits the rotation of an electric motor to a rack shaft is a pinion assist drive mechanism that meshes the rotational force of a drive gear fixed to the rotation shaft of the electric motor with a driven gear fixed to the pinion shaft. Also good.

FIG. 1 is a front view showing an electric power steering apparatus. FIG. 2 is a cross-sectional view showing a main part of the electric power steering apparatus. FIG. 3 is a block diagram showing a control system of the electric power steering apparatus. FIG. 4 is a flowchart showing a motor slip detection procedure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 14 Rack shaft 20 Electric motor 24 Drive pulley 36 Driven pulley 37 Belt (wound body)
50 Control means 55 PWM signal generation means 60 Motor slip detection means 61 Rotation detection means 62 Alarm output means

Claims (5)

In the electric power steering device that converts the rotation of the electric motor into a linear stroke of the rack shaft by a power transmission mechanism and steers the wheel connected to the rack shaft,
The number of rotations of the electric motor is integrated, the movement stroke displacement amount of the rack shaft corresponding to the integration number of rotations is calculated, and the detected movement stroke displacement amount of the rack shaft is determined as a predetermined maximum stroke displacement of the rack shaft. An electric power steering apparatus comprising: motor slip detection means that estimates that slip has occurred in the rotational force transmission system from the electric motor to the rack shaft when the amount exceeds.   The electric power steering apparatus according to claim 1, further comprising a control unit that controls the electric motor to stop when the motor slip detection unit detects the occurrence of slipping in the rotational force transmission system of the electric motor.   3. The electric power steering apparatus according to claim 1, further comprising an alarm output unit that outputs an alarm when the motor slip detection unit detects the occurrence of slip in the rotational force transmission system of the electric motor.   The driving force of the driving pulley fixed to the rotating shaft of the electric motor is driven and connected to the rack shaft via a power transmission mechanism including a driven pulley connected to the driving pulley by a winding body. The electric power steering device according to claim 1.   The electric motor according to any one of claims 1 to 3, wherein a rotational force of a driving gear fixed to a rotating shaft of the electric motor is drivingly connected to a rack shaft via a power transmission mechanism including a driven gear meshing with the driving gear. Power steering device.

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