JPS6378877A - Motor driven power steering device - Google Patents

Abstract

PURPOSE:To promote the miniaturization of an electric motor, by forming a reduction gear so as to increase its reduction ratio in accordance with an increase of a load, taken out to a signal output means, so that driving power of the electric motor is large doubled. CONSTITUTION:A reaction tear 40 is the coaxial reduction gear, having rotary axial centers of an input shaft 45, sun gear 60, carrier gear 62 and an output shaft 42 on a straight line, further the reduction gear operates so as to steplessly change its reduction ratio by changing a rotating radius (r) around the rotary axial center of a planet gear 64 which is rotated on its own axis while around the rotary axial center by frictional transmission. An actuator 44, which engages with a protruding part 78 of the reduction gear, provides a slider 90 moving a member 76 in the peripheral direction of the input shaft 45. A feed screw 92 is rotated by a pilot motor 94 transmitting its rotation by a chain, while the pilot motor 94 rotates by the amount in accordance with a driving signal of the actuator.

Description

[Detailed Description of the Invention] Presentation Retired Emperor ■Ass! The present invention relates to an electric power steering device, and particularly to downsizing of an electric motor.

As an electric power steering device for vehicles, there is one of the type described in, for example, Japanese Patent Application Laid-Open No. 58-53562. In this way, the drive torque of the electric motor, which fluctuates in accordance with the steering torque of the steering wheel, is applied via the reduction gear to the steering shaft, which is a component of the steering system connected to the steering wheel, to change the direction of the wheels. is assisted.

However, it is not always necessary to apply the same amount of deflection force to change the direction of the wheels. When the vehicle is stopped and the steering angle is near the maximum angle, when the wheels are turned, the turning force increases significantly compared to the normal state. In particular, in a forklift truck where the load on the steered wheels changes greatly between a loaded state and an unloaded state, the difference in required turning force becomes even larger. In other words, the force applied from the wheel contact area such as the road surface to resist wheel deflection is large, and the conversion rate of the force when the driver's steering force is converted into wheel deflection force and transmitted is low. In this situation, a particularly large turning force is required.

Even in such a case, the driver can rotate the steering wheel without requiring excessive steering force, and the electric motor has a practically sufficient ability to follow the steering wheel operation under normal driving conditions. In the past, the electric motor itself was capable of outputting a large driving torque. In order to obtain a large turning force using an electric motor with a low maximum drive torque that can be output, the reduction ratio of the reducer must be set large, but due to the above-mentioned demand for followability, the reduction ratio is This is because there is an upper limit. This inevitably leads to an increase in the size of the electric motor, posing the problem of an increase in installation space.

4. In order to solve the above problems, the present invention provides a reduction gear in an electric power steering device equipped with the above-mentioned steering wheel, steering system, torque detector, reduction gear, and electric motor. is capable of changing the reduction ratio, and also includes a signal output means that detects the load of the electric motor and outputs a signal of a size corresponding to the load, and a signal output means that is connected to the signal output means, A reduction ratio changing means is provided for changing the ratio to a preset reduction ratio corresponding to the magnitude of the output signal.

In the electric power steering device configured as described above, the reduction ratio of the reducer is changed to increase as the load taken out to the signal output means increases, and the electric motor The applied driving force is greatly boosted to change the direction of the wheels. Therefore, the maximum drive torque that can be output by the electric motor can be lowered compared to the conventional case, and the electric motor can be made smaller. Furthermore, since the reduction ratio is set to a small value during normal driving, the electric motor does not have insufficient ability to follow steering wheel operations by the driver, and the steering performance of the vehicle can be ensured.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment in which the present invention is applied to a forklift will be described in detail based on the drawings.

FIG. 1 is a system diagram showing an electric power steering device. In the figure, reference numeral 10 indicates a pair of rear wheels serving as steering wheels. These rear wheels 10 are each rotatably supported by knuckles 12 which are rotatably supported by a rear axle (not shown) so as to be rotatable around an axis in the substantially vertical direction, and each knuckle 12 is supported by a tie rod 14
It is connected to the output of the gearbox 16 by.

Further, in the figure, reference numeral 20 denotes a steering wheel rotated by the driver, and this steering wheel 20 is fixed to the upper end of a steering shaft 22. A torque detector 24 that detects steering torque applied to the steering wheel 20 is attached to the steering shaft 22. This torque detector 2
4 supplies a torque detection signal having a magnitude corresponding to the steering torque to a control device 30, which will be described later. On the other hand, the lower end of the steering shaft 22 is connected to the input section of the gear box 16 via a steering gear mechanism, a steering arm, and a drag link (not shown).

Therefore, the rotational movement of the steering wheel 2o is caused by the steering shaft 22. It is converted sequentially through the steering gear mechanism, the steering arm, the drag link, the input section and the output section of the gear box 16, the tie rod 14, and the knuckle 12, and acts as a turning force for the rear wheel IO. That is, in this embodiment, the steering shaft 22.
Steering gear mechanism, steering arm, drag link, gear box 16. The tie rod 14 and knuckle 12 constitute a steering system.

The gear box 16 is also connected to an output shaft 42 of a reduction gear 40, as shown in FIG. This reducer 40 includes an actuator 4 as a reduction ratio changing means.
4 are connected, and the reduction gear 40 can change the reduction ratio within a predetermined range. Further, the input shaft 45 of the reducer 40 is connected to a rotating shaft 48 of an automatic electric motor 46 that is rotated by a DC power source. The driving torque of this electric motor 46 is transmitted to the gear box 1 via the reducer 40.
6 and actuates the output section of the gear box 16 to assist in changing the direction of the rear wheels 10. moreover,
An actuator 44 and an electric motor 46 are also connected to the control device 30 as shown in FIG.

Furthermore, a reaction force is applied to the electric motor 46 in a direction that suppresses the rotation of the electric motor 46 when the rear wheel 10 changes direction, and therefore a load current flows through the electric motor 46 in accordance with the reaction force. The magnitude of this load current changes in response to the steering force applied to the rear wheels 10 by the driver. Incidentally, since the electric motor 46 is well known, a detailed explanation thereof will be omitted.

Regarding the reduction gear 40, only the reduction ratio changing mechanism that is particularly relevant to this embodiment will be described in detail. Deceleration l
! 40, as shown in FIG. 2, is an input shaft 45. Sun wheel 60. It is a coaxial reduction gear in which the rotational axes of the carrier wheel 62 and the output shaft 42 are aligned in a straight line, and the reduction ratio can be made stepless by changing the revolution radius r of the planetary wheel 64 which is rotated and revolved by friction transmission. It is a differential reducer to change.

The planetary wheel 64 has a rotation axis 67 parallel to the input shaft 45, and the rotation axis 67 is movable in parallel in the radial direction along a groove provided in the carrier wheel 62. In other words, only the orbital motion of the planetary wheel 64 is transmitted to the carrier wheel 62. Further, a disk is fixed to one end of the rotation shaft 67, and the thickness of the disk gradually decreases toward the outer circumference.

A portion of this disc is sandwiched from both sides by the support ring 70 and the flange portion 72 of the sun wheel 60 due to the elastic force of the disc spring 68. Furthermore, another part of the disk is also sandwiched between the fixed member 74 and the moving member 76 from both sides by the operating force of the moving member 76. That is, the planet wheel 64 is supported by the support ring 70. Sun wheel 60° fixed member 74 and moving member 76
It is caused to rotate and revolve by constantly frictionally engaging with the object.

At this time, the elastic force of the disk spring 68 and the operating force of the moving member 76 act on the planetary wheel 64 on both inclined sides of the planetary wheel 64, so that a component force Fl in the radial direction is applied to the planetary wheel 64.
and a component force Fu is generated. These two component forces Fl, Fu
is always kept equal by the radial movement of the planet wheel 64. The speed reducer 40 uses this principle to change the revolution radius r by moving the moving member 76 in the axial direction of the input shaft 45 to change the gap d with the fixed member 74 and increasing or decreasing the component force Fu. It is something. For example, if the function 11i1d is increased, the component force Fu will be greater than the component force F1.
becomes smaller, the planet wheel 64 is moved outward until these two component forces F1 and Fu become equal. Therefore, the revolution radius r becomes longer and the reduction ratio becomes larger.

Further, a protrusion 78 is provided on the outer peripheral surface of the movable member 76, and a plurality of balls held by a ball retainer 79 are sandwiched between the movable member 76 and the fixed cam 82. The surfaces of the moving member 76 and the fixed cam 82 that contact the balls 80 are cam surfaces 84 and 86 that are inclined in a manner complementary to each other along the circumferential direction. Therefore, if the protrusion 78 is moved in the circumferential direction of the input shaft 45, the moving member 76 is also moved in the axial direction of the input shaft 45.

The actuator 44 is connected to the reducer 4 as shown in FIG.
0, and moves the moving member 76 to the input shaft 4.
Slider 90 to be moved in the circumferential direction of No. 5 (in the direction of arrow A)
is provided.

This slider 90 is screwed onto a feed screw 92, and its rotational movement is prevented by a guide member (not shown). Therefore, the slider 90 is reciprocated in its axial direction as the feed □ screw 92 rotates forward and backward. Feed screw 9
2 is rotated by chain transmission of the rotation of the pilot motor 94, and the pilot motor 94 rotates by an amount corresponding to the actuator drive signal.

Further, the rotation of the feed screw 92 is controlled by the detection shaft 9 of the potentiometer 98 by gears 95 and 96 shown in FIG.
9. This potentiometer 98 detects the moving position of the slider 90 from the amount of rotation of the detection shaft 99, and outputs a detected position signal that is a signal corresponding to the amount of rotation.

Next, the control device 30 will be explained based on the block diagram shown in FIG. The control circuit 30 is the motor drive circuit 1
00. It is composed of differential amplifiers 102 and 104 and an actuator drive circuit 106.

A torque detection signal is input from the torque detector 24 to the motor drive circuit 100, and the motor drive circuit 100 supplies the electric motor 46 with a motor drive current having a magnitude corresponding to the torque detection signal. The electric motor 46 has a take-out unit 101 that takes out a load signal indicating the magnitude of the load current generated.
is provided, and this extraction section 101 is connected to the differential amplifier 10.
Connected to 2. A predetermined reference value signal is inputted to the differential amplifier 102 together with the load signal, and a target position signal indicating the target movement position of the slider 90 is sent to the differential amplifier 104 according to the magnitude of these inputs. supply A detected position signal from the potentiometer 98 is further input as a feedback signal to the differential amplifier 104, and a movement amount signal corresponding to the difference in magnitude between these two forces is supplied to the actuator drive circuit 106.

As a result, actuator drive circuit 106 supplies pilot motor 94 with an actuator drive signal instructing the required rotation amount of pilot motor 94 corresponding to the movement amount signal. That is, in this embodiment, the differential amplifiers 102 and 104 and the actuator drive circuit 106
constitutes a signal output means for outputting a signal having a magnitude corresponding to the load of the electric motor 46.

Next, the operation of the device of this embodiment will be explained.

In response to the steering torque applied to the steering wheel 20 shown in FIG. 1, the torque detector 24 provides a torque detection signal to the motor drive circuit 100 shown in FIG. The motor drive circuit 100 supplies the electric motor 46 with a motor drive current having a magnitude corresponding to the torque detection signal. Therefore, the electric motor 46 applies a drive torque corresponding to the motor drive current to the gear box 16 via the reduction gear 40 to assist in changing the direction of the rear wheels 10.

At this time, the load signal of the electric motor 46 is transmitted to the differential amplifier 102.
is input. The reduction ratio of the reduction gear 40 is set in advance so as to have the relationship shown in FIG. 6 with respect to this load signal. That is, the reduction ratio remains constant until the load signal exceeds the reference value signal, but is set to increase proportionally after the load signal exceeds the reference value signal.

Therefore, the differential amplifier 102 supplies the differential amplifier 104 with a target position signal instructing the movement position of the slider 90 at which the above-mentioned reduction ratio corresponding to the load signal can be obtained. Differential amplifier 104 supplies a movement amount signal of slider 90 to actuator drive circuit 106 based on the target position signal and the detected position signal from potentiometer 98 . The actuator drive circuit 106 supplies an actuator drive signal to the pilot motor 94 based on the input movement amount signal, rotates the pilot motor 94 by a predetermined amount, moves the slider 110 to a predetermined position, and adjusts the reduction ratio to an appropriate size. change to

In this way, the turning force of the rear wheels 10 provided by the electric motor 46 is boosted as necessary, allowing the driver to change the direction of the rear wheels 10 without applying excessive steering torque to the steering wheel 20. Directions can be made.

Although one embodiment of the present invention has been described above based on the drawings,
The invention is also possible in other embodiments. For example, in this embodiment, the reduction gear is capable of changing the reduction ratio continuously, but it is also possible to employ a reduction gear and a control device that can change the reduction ratio in steps. Furthermore, stabilization of the operation of the actuator 44 is attempted by setting a reference value of the load signal and ignoring minute fluctuations below the reference value of the load signal, but this reference value can be changed as appropriate.

In addition, although no specific examples will be given, the present invention can be applied to electric power steering devices for vehicles other than forklifts, and various modifications and improvements can be made based on the knowledge of those skilled in the art. It can be implemented.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an electric power steering device according to an embodiment of the present invention. FIG. 2 shows an electric motor used in the above embodiment device. 3 is a sectional view taken along line I-1 in FIG. 2, and FIG. 4 is a sectional view taken along line 1--2 in FIG. 3. FIG. FIG. 5 is a block diagram showing the control device and its related parts used in the apparatus of the above embodiment. FIG. 6 is a graph showing the relationship between the preset load signal and the reduction ratio of the reduction gear in the apparatus of the above embodiment. 10: Rear wheel 16: Gear box 20 Steering wheel 22 Steering shaft 24: Torque detector 30: Control device 40: Reducer
44: Actuator 46: Electric motor 1
00: Motor drive circuit 102: Differential amplifier 104:
Differential amplifier 106: Actuator drive circuit Applicant: Toyoda Automatic Loom Works, Ltd.

Claims (1)

[Scope of Claims] A steering system that converts steering torque applied to the steering wheel into a turning force for changing the direction of the wheel is connected to a steering wheel rotated by a driver, and a steering system that converts steering torque applied to the steering wheel into a turning force for turning the wheel is connected to the steering wheel. Electric power steering is equipped with a torque detector that detects torque and is connected to an electric motor via a speed reducer, and a current corresponding to the steering torque is supplied to the electric motor to assist in changing the direction of the wheels. In the apparatus, the reduction gear is capable of changing a reduction ratio, and the signal output means detects the load of the electric motor and outputs a signal of a magnitude corresponding to the load, and the signal output means includes: 1. An electric power steering device comprising: a reduction ratio changing means connected to the reduction gear for changing the reduction ratio of the reduction gear to a preset reduction ratio in accordance with the magnitude of the output signal.