JPS60154955A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To smoothly move a rack axis with small turning force of a motor by rotating the motor round the rack axis and transmitting the turning force of the motor to the rack axis through a screw connection means. CONSTITUTION:When steering force exceeds a preset value, a control unit 20 calculates the proper output torque value of a brushless motor 8 based on car speed signals and the steering force signals and supplies the driving current that corresponds to the proper output value to a stator coil 11. A rotary axis 9 rotates to the side that corresponds to the steering direction depending on the magnitude of the driving current and a ball nut 17 is driven in rotation through a planetary gear 16 by the turning force. The turning force is transmitted to a rack axis 2 through a ball 19 and the rack axis 2 moves in the axial direction, then left and right driving wheels are steered in the steering direction. As a result, the power assist of a steering device is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric power steering device that uses an electric motor to assist the steering force of a vehicle such as an automobile.

[Prior art]

As a conventional electric power steering device, for example,
There is one described in Japanese Patent No. 7-47251. Its features include a servo motor that rotates by an electric signal generated by converting the displacement generated by a mechanically provided displacement generating means according to the operating resistance using a sensor and a servo device;
Alternatively, the pulse motor is mounted on the outer periphery of the steering gear device, with the rotary drive shaft connected to the opposite end of the steering wheel or the output shaft end of the steering gear device.

This converts the rotational torque of the steering shaft that should be increased into an electrical signal, and transmits the rotational driving force of the electric motor that operates accordingly to the steering gear device, thereby reducing the operating force of the steering wheel. There is.

[Problems with conventional technology]

Such conventional electric power steering devices have a structure in which the electric motor is fixed to the outside of the steering gear box. As a result, the electric motor protrudes outward, which often interferes with other equipment due to space constraints (for example, it is often necessary to change the shape of the engine room or tie rod, etc.). Not only is it difficult to use in common among different car models, but
There was a problem that it could not be replaced with the current power steering device.

Furthermore, some conventional electric power steering devices use gears to transmit power from the electric motor to the rank shaft or sector gear to increase the output of the electric motor. There is a problem in that the steering wheel does not return easily due to meshing friction force and the like.

[Purpose of the invention]

This invention was made by focusing on these conventional problems, and solved the above problems by using a screw shaft as the rank shaft and a structure in which the electric motor rotates around this rank shaft. It is intended to.

[Structure of the invention]

According to the present invention, an electric motor has a cylindrical rotating shaft, a rank shaft having a threaded portion on the outer periphery is passed through a hole in the rotating shaft, and the rank shaft and the rotating shaft are screwed together. The present invention relates to an electric power steering device that is connected to each other via a means and that moves the rack shaft in its axial direction by rotation of the rotation shaft.

〔Example〕

The present invention will be explained below based on illustrated embodiments.

FIGS. 1 to 3 are diagrams showing one embodiment of the present invention.

First, the structure will be described. Reference numeral 1 (not shown in FIG. 1) is a steering gear box, and a shaft 2 passes through a hole 1a of the steering gear box 1. Rack axis 2
A rack 2a and a ball screw 2b, which is a threaded portion, are provided at a predetermined interval in the axial direction, and a pinion 3a of a pinion shaft 3 inserted into a steering gear box 1 meshes with the rack 2a. .

A steering shaft 4 is connected to the protruding end of the pinion shaft 3, and rotation of a steering wheel 5 fixed to the upper end of the steering shaft 4 causes the rank shaft 2 to move in its axial direction through the operation of the pinion shirts 1 to 3. and slides to the side corresponding to the rotational direction.

A steering force detector 6 is composed of, for example, a strain gauge attached to the steering shaft 4 and a Wheatstone bridge incorporating this strain gauge, and corresponds to the direction of rotation of the steering shaft 4 and the magnitude of its torsion angle. The generated signal is sent to the control device 20.

Further, a chamber 7 is provided inside the steering gear box 1.
This chamber 7 houses a brushless morph 8, which is an electric motor, and a ball nut 17, which has a groove with a circular cross section on the circumferential surface of the hole, through which the rank shaft 2 passes. .

The brushless morph 8 consists of a rotating shaft 9 which has a cylindrical shape and through which the rank shaft 2 having a slightly smaller diameter passes through, and a rotating shaft 9 which is fixed to the outer periphery of the rotating shaft 9 and arranged in a ring shape in the circumferential direction. Armature 1 consisting of a plurality of permanent magnets installed
0, a ring-shaped stator coil 11 disposed outside the armature 10 and fixed to the steering gear box 1, and a control circuit 12 consisting of a thyrisk commutator and a distributor.

The rotating shaft 9 is rotatably supported by the steering gear box 1 via two bearings 13, and a sun gear 14 is formed on the outer periphery of one end in the axial direction. 15 is a ring gear formed in the steering gear box 1, and a plurality of planetary gears 16 are commonly meshed with this ring gear 15 and the sun gear 14. The planetary gear 16 is rotatably supported on the brushless morph 8 side of the ball nut 17.

The two ball nuts 17 are rotatably supported on the steering gear box 1 via two bearings 18 with their axial movement restricted. The ball screw 2b provided on the rank shaft 2 faces inside this ball nut 17, and a plurality of balls 19 are inserted between the two members 2 and 17 between the groove and the ball screw 2b.
and are interposed in common engagement with each other. Above ball screw 2
b, the ball nut 17, and the ball 19 constitute a ball screw which is a specific example of the threaded coupling means.

Thus, when the brushless morph 8 is driven to rotate the rotating shaft 9, the brushless gear 16 meshing with the sun gear 14 rotates and revolves around the sun gear 14 in the same direction, thereby rotating the ball nut 17 in the same direction as the rotating shaft 9. . The rotational force of the ball nut 17 is transmitted to the rank shaft 2 via the balls 19, thereby moving the rack shaft 2 in its axial direction to the side corresponding to the rotation direction of the rotary shaft 9.

Drive control of the brushless morph 8 is performed by a control signal from a control device 20 that is supplied to the stator coil 11 via a motor drive circuit 21 and a control circuit 12. In addition to the steering force signal from the steering force detector 6, a vehicle speed signal corresponding to the vehicle speed from the vehicle speed detector 22 is input to the control device 20.

The vehicle speed detector 22 includes, for example, a rotation detector closely opposed to the output shaft of a transmission, and a frequency-voltage converter that converts a pulse signal from the rotation detector into an analog voltage output corresponding to the rotation speed of the output shaft. It consists of

Further, the control device 20 takes in the current flowing from the motor drive circuit 21 to the control circuit 12, and detects the actual motor torque value at that time by looking at the current value.

The control device 20 is composed of a processing device such as a microcomputer, and performs control as shown in the flowchart of FIG. 3, for example. That is, the operation of the control device 20 is started by turning on the ignition key switch and driving the engine.

First, the vehicle speed is read using the steering wheel and knob 1, and then the process moves to step 2 to read the steering force. Then, the process proceeds to step 3, where it is determined whether or not the read steering force is greater than a preset reference value. As a result, if the detected steering force is greater than the reference value, the process proceeds to step 4.

In step 4, it is determined whether or not the steering direction is to the right, and if the result is that the steering direction is to the right, the process proceeds to step 5, where an output torque management table stored in a predetermined storage area is referred to, Then move on to step 6,
An appropriate value of the output torque T is calculated based on the detected vehicle speed and the detected steering force.

This output torque management table stores the relationship between steering force and motor output torque using vehicle speed as a parameter.

Next, in step 7, a drive current, which is a control signal corresponding to the calculated output torque value, is output to the stator coil 11 via the motor drive circuit 21 and the control circuit 12. Next, move to step 8 and create brushless morph 8.
The actual output torque T1 of the motor is read, and further, in step 9, whether or not the actual output torque TI of the motor is within a predetermined range with respect to the appropriate output torque T (α is a predetermined deviation set in advance). value), and if the actual output torque T1 is within a predetermined range, proceed to step 10,
Determine whether control is complete.

This control is completed when the ignition key switch is turned off and the engine is stopped.

If it is determined in step 4 that the steering direction is not to the right, the process moves to step 11, refers to the output torque management table for left steering which is stored in a predetermined storage area, and then proceeds to step 11. Moving on to 6,
The appropriate value of the output torque of the brushless morph 8 is calculated in the same manner as described above.

Further, in step 9, if the actual output torque T1 is not within the predetermined range, the process moves to step 12, and the output value is corrected. In this case, when the actual output torque T1 exceeds the predetermined range on the high side, the target value of the appropriate output torque T is decreased, and when the actual output torque T1 exceeds the predetermined range on the low side, the appropriate output torque Correct to increase the target value of T.

Next, the effect will be explained.

When the ignition key switch is turned on to drive the engine, the control device 20 starts operating at the same time, and a vehicle speed signal from the vehicle speed detector 22 is supplied to the control word W20. From this state, when the steering wheel 5 is rotated to the right or left and steered in either direction, a steering force signal corresponding to the steering force and steering direction at that time is supplied from the steering force detector 6 to the control 2 position 20. be done.

The control device 20 calculates an appropriate value of the output torque of the brushless morph 8 to assist the steering force based on the vehicle speed signal and the steering force signal when the steering force is equal to or higher than a set value, and calculates the appropriate output torque. A drive current corresponding to the value is sent to the stake coil 1 via the motor drive circuit 21 and the control circuit 12.
Supply to 1.

In this case, the control device 20 determines the steering direction based on the steering force signal, and adjusts the stake coil 11 according to the steering direction.
For example, when steering to the right, the rotation axis 9
The same shaft is rotated forward, and when steering to the left, the same shaft is reversed.

When a drive current is supplied to the stator coil 11, the rotating shaft 9 rotates in a direction corresponding to the steering direction according to the magnitude of the drive current, and the rotational force rotates the ball nut 17 via the planetary gear 16. . ball nut 1
The rotational force transmitted to 7 is transmitted to the rank shaft 2 via the ball 19, thereby generating an axial thrust on the rank shaft 2, which acts in a direction to assist the steering force. As a result, the rank shaft 2 moves in its axial direction, and the left and right drive wheels connected to both ends of the rack shaft 2 are steered in the steering direction, thus power assisting the steering device.

In this case, since the brushless morph 8 and the rack shaft 2 are connected via a ball screw, the rack shaft 2 can be easily moved in the axial direction with a small force, and the brushless morph 8 can be made smaller. Furthermore, by increasing the lead angle α of the ball screw shown in FIG. 2, it is possible to prevent the sliding of the rank shaft 2 from being suppressed by the frictional force, and to improve the return of the steering wheel 5. This can improve the steering feel.

Furthermore, since the brushless morph 8 is fitted onto the rank shaft 2 and the motor is configured to rotate around the rank shaft 2, the electric motor does not protrude significantly outward, and the shape of the engine room and tie rod can be easily It is possible to obtain a suitable steering feel according to the vehicle speed without making many changes to the steering system.

〔Effect of the invention〕

As described above, in the present invention, the electric motor rotates around the rack shaft, and the rotational force of the electric motor is transmitted to the rack shaft via the screw coupling means. Therefore,
The rack shaft can be moved smoothly with the small rotational force of the electric motor. Furthermore, since the electric motor does not protrude significantly outward, there is little need to change the shape of the engine or the shape of the tie rod, and it is possible to create a power steering device with excellent steering feel without making many changes to the current steering system. The effect is that it can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of the essential parts of FIG. 1, and FIG. 3 is an example of a flowchart of a control device according to the present invention. FIG. 1... Steering gear box, 2...
・・Rank shaft, 2b・・・・Ball screw (threaded part)
, 6... Steering force detector, 8... Brushless morph (electric motor), 9... Rotating shaft, 10...
... Armature, 11 ... Stator coil, 12 ... Control circuit, 14 ... Sun gear, 15 ... Ring gear, 16 ...・
・Planetary gear, 17... Ball Nand, 1
9...Ball, 20...Control device, 2
2...Vehicle speed detector patent applicant Nissan Motor Co., Ltd. Representative Patent attorney Tetsuya Mori Representative Patent attorney Yoshiaki Naito Patent attorney Shimizu Masaru Patent attorney Baize Horide

Claims (1)

[Claims] The electric motor has a cylindrical rotating shaft, a rank shaft having a threaded portion on the outer periphery passes through a hole in the rotating shaft, and the rank shaft and the rotating shaft are connected via a screw coupling means, and the An electric power steering device characterized in that the rank shaft is moved in its axial direction by rotation of a rotating shaft.