JP4349334B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an improvement in the performance of an electric power steering apparatus that assists a force required to operate a steering wheel of a vehicle with a rotational force of an electric motor.

  As a power steering device for a vehicle used for assisting a steering force, an electric motor configured to assist the steering force of a steering wheel by a driver using the rotational force of an electric motor (hereinafter referred to as “motor”). A type power steering device is known.

  As an example of this type of electric power steering apparatus, Japanese Patent Publication No. 7-25311 discloses a power steering apparatus that employs a rack and pinion type motion conversion mechanism that converts motion into linear motion.

  FIG. 8 is an enlarged cross-sectional view of a conventional rack and pinion type motion conversion mechanism. In this mechanism, the pinion shaft 86 is formed with pinion teeth 86a on the outer peripheral surface of the end portion thereof, and the rack shaft 81 is formed with a flat portion in the axial direction in the vicinity of one end portion thereof, and the flat portion extends over its entire length. Rack teeth 81a are formed. The pinion teeth 86a and the rack teeth 81a mesh with each other to convert the rotational motion into a linear motion. The rack teeth 81a are screwed so that the gear ratio with respect to the pinion teeth 86a becomes small at a position in the direction in which the vehicle goes straight and the gear ratio becomes large at a position where the steering angle is large, so that the rotation output is relatively small. A device has been devised to keep the steering force constant despite the small electric motor.

  In this rack-and-pinion type motion converting mechanism, the rack shaft 81 is pressed by the biasing force of the coil spring 89 that abuts one end of the pressing member 80 in a substantially cylindrical member, and the engagement between the rack teeth 81a and the pinion teeth 86a is maintained. ing. By this engagement, the rotation of the pinion shaft 86 is converted into a linear motion in the axial direction of the rack shaft 81, and the pressing member 80 slides on the outer peripheral surface of the rack shaft 81. Therefore, in this structure, the sliding surface is extremely worn, and the pressing force (biasing force) by the coil spring 89 is limited. For this reason, in an electric power steering mechanism such as a pinion-assisted electric power steering in which a relatively large torque is applied to the pinion shaft, a necessary pressing force cannot be obtained, and from around the meshing surface of the pinion teeth 86a and the rack teeth 81a. There is a disadvantage that abnormal sounds such as rattle sounds are generated.

  In general, an electric power steering apparatus connects a rotating shaft of a steering wheel and a pinion shaft of a rack and pinion type motion conversion mechanism by a joint. The electric power steering apparatus includes a column type electric power steering apparatus in which a motor and a speed reduction mechanism of the motor are closer to the steering wheel than the joint, and a rack and pinion mechanism in which the motor and the speed reduction mechanism of the motor are more than the joint. There is a pinion type electric power steering device on the side.

  When increasing the output of an electric power steering device, there is a problem that the size of the motor is limited due to layout and the like, and the output of the motor is also limited. In order to solve this problem, a method has been proposed in which the efficiency of the motor is effectively increased by increasing the efficiency of the mechanical system, particularly the rack and pinion motion conversion mechanism. As this method, in the rack and pinion type motion converting mechanism, a technique using a rotatable roller as a pressure pad portion that presses the rack shaft against the pinion shaft (hereinafter referred to as “rolling type rack and pinion motion converting mechanism”). ) Has been conceived. According to the rolling rack and pinion motion conversion mechanism, the mechanical efficiency can be greatly improved when a high load is applied between the rack shaft and the pinion shaft.

  However, when a rolling rack and pinion motion conversion mechanism is combined with a column type electric power steering device or a pinion type electric power steering device, the motor does not respond to kickback from the road surface. The rack and pinion mechanism is overloaded as compared with the electric power steering apparatus.

  Furthermore, in this case, since the sliding surface is rolling, the attenuation of the kickback force is worse than that of the conventional sliding type, so that there is a problem that rattle noise is likely to occur.

  Furthermore, in this case, the other purpose of introducing the rolling rack and pinion motion conversion mechanism is to improve the handle return characteristics and the on-center feeling by reducing the frictional force, but the influence of the frictional force of the motor is influenced by the rolling rack and pinion. Since it is larger than the improvement by the pinion motion conversion mechanism, there is a problem that the effect to achieve the purpose is not obtained.

  The present invention has been made under the circumstances described above, and an object of the present invention is to prevent an excessive load from being generated in the rack and pinion motion conversion mechanism, to suppress the generation of rattle noise, An object of the present invention is to provide an electric power steering apparatus that can reduce the influence of frictional force.

An object of the present invention relates to an electric power steering apparatus including a steering mechanism that gives a steered wheel a desired steering angle and a motor that assists the steering force of the steering wheel by a driver. This is achieved by inserting an elastic body into the mechanism path to the output shaft of the motor and controlling the motor by a control unit that performs friction compensation control.

The above object of the present invention also relates to an electric power steering apparatus comprising a steering mechanism for giving a desired steering angle to a steered wheel and a motor for assisting a steering force of the steered wheel by a driver. A reduction mechanism between the motor and the motor, and an elastic body is inserted into a mechanism path from the output shaft of the motor to the reduction mechanism, and the motor is controlled by a control unit that performs friction compensation control. Is achieved more effectively.

The above-mentioned object of the present invention can be achieved more effectively by configuring the speed reduction mechanism with a worm connected to the motor and a worm wheel connected to the rudder wheel shaft.

Further, the above object of the present invention is achieved more effectively by arranging a torque sensor on the rudder wheel shaft and performing friction compensation control by a detection signal from the torque sensor.

Further, the above object of the present invention can be achieved more effectively by making the friction compensation control the friction compensation control of a motor.
The above-mentioned object of the present invention is more effectively achieved by performing the friction compensation control by adding a value proportional to the derivative of the steering torque signal to the steering assist command value.

The above-mentioned object of the present invention can be achieved more effectively by making the steering mechanism a rack and pinion type motion conversion mechanism.
Furthermore, the above-mentioned object of the present invention is more effectively achieved by replacing the rack and pinion type motion converting mechanism with a rolling type rack and pinion type motion converting mechanism.

  According to the present invention, in the electric power steering apparatus using the rolling rack and pinion motion conversion mechanism, the elastic body is inserted in the path from the pinion shaft of the rolling rack and pinion motion conversion mechanism to the output shaft of the motor. Provided is an electric power steering device that can prevent an excessive load from being generated in a rolling rack and pinion motion conversion mechanism, suppress the occurrence of rattle noise, and reduce the influence of the frictional force of the motor. be able to.

BEST MODE FOR CARRYING OUT THE INVENTION

  According to the present invention, when the rolling rack and pinion motion conversion mechanism 4 is used in the column type electric power steering apparatus as shown in FIG. 7 or the pinion type electric power steering apparatus as shown in FIG. -Since an elastic body having a vibration absorbing property is inserted in the path from the pinion shaft 6 of the pinion motion conversion mechanism 4 to the motor 41 that is a power steering drive source, the pinion shaft 6 moves relative to the motor 41. Therefore, it is possible to prevent an excessive load from being generated in the rolling rack and pinion motion conversion mechanism 4.

  Both the column type electric power steering apparatus as shown in FIG. 7 and the pinion type electric power steering apparatus as shown in FIG. 6 are provided between the motor 41 and the worm wheel 3 that is a reduction mechanism of the motor 41. The effect of the present invention can be obtained by inserting an elastic body having vibration absorption properties. In the column type electric power steering apparatus as shown in FIG. 7, the joint 51 disposed between the rotating shaft of the worm wheel 3 and the pinion shaft 6 of the rolling rack and pinion motion converting mechanism 4 has vibration absorption. The effect of the present invention can be obtained by inserting an elastic body.

  In addition, according to the present invention, the damping action of the elastic body having vibration absorption compensates for the deficiency of the damping action of the kickback force of the rolling rack and pinion motion conversion mechanism 4, thereby preventing the generation of rattle noise. be able to.

  Furthermore, according to the present invention, an elastic body having vibration absorption is interposed between the motor 41 and the speed reduction mechanism of the motor 41, so that the rotation axis of the motor 41 and the pinion shaft 6 are For example, even in a situation where the motor 41 is stopped by the frictional force, the steering wheel shaft 31 can be rotated in conjunction with the pinion shaft 6, and the motor 41 can be rotated. The influence of the frictional force can be reduced, and the effect of the technology combining the rolling rack and pinion motion conversion mechanism 4 and the column type electric power steering device or the pinion type electric power steering device can be utilized.

  Furthermore, according to the present invention, the friction compensation control using the torque sensor signal is such that in the conventional configuration, the road surface information is blocked by the rack and pinion motion conversion mechanism 4 or the motor 41, and the road surface information is not transmitted to the torque sensor. Therefore, according to the configuration of the present invention, the road surface information is transmitted to the torque sensor, and the friction of the motor can be compensated by the friction compensation control using the torque sensor signal. It becomes possible, and generation | occurrence | production of the rattle sound by a motor puffing can be suppressed effectively.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a front view showing a main part of a front wheel steering mechanism including an electric power steering apparatus according to an embodiment of the present invention.

  In FIG. 1, the steering wheel shaft 31 is fixed to a predetermined position in the vehicle interior in a state where the lower portion is inclined forward, and is supported in a cylindrical housing 32 so as to be rotatable about an axis. A steered wheel (not shown) is fixed to the upper end portion of the steered wheel shaft 31 protruding a predetermined length from the upper part of the housing 32.

  The rack-and-pinion type motion conversion mechanism 4 includes a cylindrical rack shaft case 36 that has a longitudinal direction in the left-right direction of the vehicle and is installed almost horizontally in the engine room at the front of the vehicle. The rack shaft 13 is inserted into the rack shaft case 36 so as to be substantially aligned with the shaft center so as to be movable in the axial length direction. The rack shaft 13 is supported in the rack shaft case 36 at an angle with respect to the axis of the rack shaft 13. And the pinion shaft 6 and the like.

  FIG. 2 is a sectional view showing a rolling rack and pinion type motion conversion mechanism in the electric power steering apparatus according to the embodiment of the present invention.

In FIG. 2, the upper part is an input shaft 18 through which the rotation of the steering wheel is transmitted from the steering wheel shaft 31 side via the universal joint 19 (see FIG. 1). It is attached to. Further, the torque sensor unit 1 is connected to the input shaft 18 and plays a role of detecting a steering system load and transmitting the torque signal to an ECU (electric control unit, not shown).

  When an electric current calculated and output from the ECU based on the vehicle speed signal and the torque signal is applied, the electric motor (not shown) rotates, and the rotation is transmitted to the worm 2. The worm 2 is disposed coaxially with the electric motor that assists the steering force. Furthermore, the rotational force of the worm 2 is decelerated by the worm wheel 3 (see FIG. 3) fitted on the pinion shaft 18 and the torque is increased to assist the rotational motion of the pinion shaft 6.

  The pinion shaft 6 is supported by bearings 5 and 15 inside the gear box. Pinion teeth 6a are formed on the outer periphery of the pinion shaft 6, and the rack teeth 13a of the rack shaft 13 as a steering mechanism mesh with the pinion teeth 6a, and the rack shaft 13 is displaced in the axial length direction (front and back direction in FIG. 2). Thus, a desired steering angle is finally given to a steered wheel (not shown) via a tie rod 21 (see FIG. 1).

  A part of the end of the rack shaft 13 is semicylindrical in cross section, and rack teeth 13 a are screwed into the flat portion 13 b in the axial direction of the rack shaft 13. When the rack teeth 13 a and the pinion teeth 6 a mesh with each other, the rotational motion of the pinion shaft 6 is converted into the linear motion of the rack shaft 13. In order to maintain this meshing relationship, the pressure pad portion 20 applies a pressing force to the meshing portion via the rack shaft 13. Further, a mechanism for applying a pressing force to the meshing portion is provided in a substantially cylindrical housing 16 that protrudes from the gear box 4 in a direction orthogonal to the axial direction of the pinion shaft 6.

  The pressure pad portion 20 includes a roller 10, a needle bearing 11, a pin shaft 12, and a bearing holder 14, and with respect to the pinion shaft 6 with a predetermined pressing force so as to maintain the engagement between the pinion teeth 6 a and the rack teeth 13 a. The rack shaft 13 is pressed. The pressure pad portion 20 is configured such that the pin shaft 12 is positioned at a predetermined position by the bearing holder 14 and the roller 10 can be rotated around the pin shaft 12 as the rack shaft 13 moves in the axial direction. . In this embodiment, only the roller 10 slides on the outer peripheral surface 13 c of the rack shaft 13. That is, the roller 10 is configured to roll with respect to the rack shaft 13.

  In a state where the pressure pad portion 20 is housed in the housing 16, the pressure pad portion 20 including the bearing holder 14, the pin shaft 12, the needle bearing 11, and the roller 10 is integrally formed in the housing 16 in the axial direction thereof. It is movable.

  Further, a coil spring 9, which is an elastic member, is disposed in the housing 16 on the opposite side of the pressure pad portion 20 from the rack shaft 13. One end of the coil spring 9 for applying a pressing force to the pressure pad portion 20 is in contact with the pressure pad portion 20 (the surface of the bearing holder 14), and the other end is screwed together with the lock nut 7 to the end portion of the housing 16 It is in contact with the screw 8.

  Therefore, by adjusting the adjustment screw 8 and moving it in the axial direction, the pressing force applied to the pressure pad portion 20 by the coil spring 9 extending inside the housing 16 can be adjusted.

  According to such a rolling rack and pinion motion conversion mechanism, the mechanical efficiency can be greatly improved when a high load is applied between the rack shaft and the pinion shaft.

  FIG. 3 is a partial cross-sectional view showing a motor serving as a power steering drive source and a reduction mechanism for the motor in the electric power steering apparatus according to the embodiment of the present invention. The feature of this embodiment is that rubber 60, which is an elastic body, is arranged between both end portions of the worm 2 and the worm bearing 35 so that the worm 2 in the speed reduction mechanism of the motor 41 can move in the worm axis direction. This is the point.

  In the elastic range (movable range) of the rubber 60, the rotation of the worm wheel 3 is displaced in the axial direction of the worm until the torque generated in the worm 2 overcomes the frictional force and inertia of the motor 41, and the rotation of the motor 41 and the pinion It does not interlock with the rotation of the worm wheel 3 interlocked with the shaft 6. That is, when the worm wheel 3 receives a kickback from the road surface, the worm 2 is slid and the rubber 60 absorbs the kickback impact.

  According to such a structure, in the movable range of the worm 2 by the rubber 60, the kickback force can be released in the rotational direction of the pinion shaft 6 without being focused on the motor 41, so that the load on the rack and pinion mechanism is increased. It can prevent concentration. Further, according to such a structure, since the vibration damping action of the rubber 60 compensates for the lack of the vibration damping action, which is a drawback of the rolling rack and pinion motion conversion mechanism, the generation of rattle noise can be prevented.

  FIG. 4 is a block diagram showing a control unit 40 which is another embodiment of the present invention and performs friction compensation control of a motor in an electric power steering apparatus.

  The control unit 40 sets a value proportional to the derivative of the steering torque signal with respect to the assist amount (steering assist command value) for the purpose of improving the assist torque response and the stability of the torque control system. Add to increase. A signal obtained by differentiating the torque amount in this way is added to the assist amount. Further, when the steering torque is large and the steering wheel returns, that is, a negative gain is applied when the steering angle θ decreases, a sudden decrease in the assist amount (steering assist command value) is prevented, resulting in a high torque. A large hysteresis characteristic is given in the region, and a small hysteresis characteristic is given in the low torque region near the neutral point.

  That is, the control unit 40 performs friction compensation control based on the torque signal Tr that is a torque detection value for the purpose of compensating for the influence of friction of the motor 41. This friction compensation control speeds up the responsiveness of torque control in the vicinity of the center where the steering torque is small, and acts in the direction of suppressing the torsion bar detecting the torque to a minimum. On the other hand, the friction of the motor 41 acts in the direction of increasing the torsion bar torsion. Therefore, if the friction of the motor 41 can be detected as a twist of the torsion bar, the friction compensation can be performed by the friction compensation control by the control unit 40.

  However, since the torsion bar is disposed closer to the handle than the motor 41, friction compensation can be made for input from the handle, but compensation for input from the road surface such as kickback is difficult. Thus, the rattle noise of the rack and pinion motion conversion mechanism 4 cannot be reduced by the friction compensation control.

However, in the elastic region of the rubber 60, which is an elastic body as shown in FIG. 3, the input from the road surface can be detected by the torque sensor 1 , and the friction compensation control is also effective for the input from the road surface. Once the friction compensation control is performed by the control unit 40, the friction of the motor 41 is compensated and the input from the road surface can be detected by the torque sensor 1 . In other words, the rubber 60 and the friction compensation control allow the kickback force to escape from the rack and pinion type motion conversion mechanism 4 to the handle side beyond the elastic range of the rubber 60. Furthermore, by tuning the friction compensation control by the control unit 40, the rattle noise of the rack and pinion type motion conversion mechanism 4 can be suppressed, and tuning for appropriately transmitting road surface information to the steering wheel can be performed.

  The rubber 60 which is an elastic body as shown in FIG. 3 is the above-described rolling rack and pinion motion conversion regardless of where it is placed from the speed reduction mechanism of the motor 41 to the mechanism causing the friction or inertia of the motor 41. The effect of preventing excessive load on the mechanism, the effect of preventing the generation of rattle noise by compensating for the deficiency of the kickback force damping mechanism of the rolling rack and pinion motion conversion mechanism, and the influence of the frictional force of the motor The effect to reduce can be acquired.

  FIG. 5 is a front view showing a main part of a front wheel steering mechanism including an electric power steering device according to another embodiment of the present invention. In this embodiment, rubber 60, which is an elastic body as shown in FIG. 3, is arranged at a joint 51 that couples the pinion shaft 6 of the rack and pinion motion conversion mechanism 4 and the output shaft 50 of the reduction mechanism of the motor 41. It is.

It is a front view which shows the principal part of the front-wheel steering mechanism containing the electric power steering device which concerns on embodiment of this invention. It is sectional drawing which shows the rolling rack and pinion type | formula motion conversion mechanism in the electric power steering apparatus which concerns on embodiment of this invention. It is a fragmentary sectional view showing a motor used as a drive source of power steering in an electric power steering device concerning an embodiment of the present invention, and a reduction mechanism of the motor. It is a block diagram which shows the control unit which performs the friction compensation control of the motor in the electric power steering device which is other embodiment of this invention. It is a front view which shows the principal part of the front-wheel steering mechanism containing the electric power steering device which is other embodiment of this invention. It is a front view which shows the pinion type electric power steering device which is other embodiment of this invention. It is a front view which shows the column type electric power steering device which is other embodiment of this invention. It is sectional drawing which shows the rack and pinion type | formula motion conversion mechanism of the conventional electric power steering apparatus.

Explanation of symbols

2 Worm 3 Worm Wheel 4 Rack / Pinion Motion Conversion Mechanism 6 Pinion Shaft 10 Roller 13 Rack Shaft 18 Input Shaft 19 Universal Joint 20 Pressure Pad Section 31 Steering Wheel Shaft 36 Rack Shaft Case 40 Control Unit 41 Motor 42 Spline 43 Bush 51 Joint 60 Rubber

Claims (6)

In an electric power steering apparatus comprising a steering mechanism for giving a desired steering angle to a steered wheel and a motor for assisting a steering force of the steered wheel by a driver,
A speed reduction mechanism comprising a worm coupled to the motor and a worm wheel coupled to the steering wheel shaft;
An elastic body disposed on the shaft of the worm ;
A control unit that performs friction compensation control based on a detection signal from a torque sensor disposed on the rudder wheel shaft ,
The worm shaft is displaceable on both sides in the axial direction within the range of the elastic region of the elastic body, and
The electric power steering apparatus according to claim 1, wherein the control unit is capable of performing friction compensation with respect to inputs in both directions from the steering wheel side and the road surface side . The electric power steering apparatus according to claim 1 , wherein the friction compensation control is a friction compensation control of a motor. 3. The electric power steering apparatus according to claim 1 , wherein the friction compensation control is performed by adding a value proportional to a derivative of a steering torque signal to a steering assist command value. 4. The electric power steering apparatus according to claim 1 , wherein the steering mechanism is a rack and pinion type motion conversion mechanism. 5. The electric power steering apparatus according to claim 4 , wherein the rack and pinion type motion conversion mechanism is a rolling type rack and pinion type motion conversion mechanism. The electric power steering apparatus according to any one of claims 1 to 5, wherein the elastic body is disposed at both axial ends of the worm.

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