JPH02290774A - Power steering device - Google Patents

Abstract

PURPOSE:To suppress the excessive operation in the return control for a steering wheel by setting the returned angular speed for the steering wheel according to the steering angle and car speed and controlling the electric current which flows in a motor so that the actual angular speed of the steering wheel accords with the set angular speed. CONSTITUTION:In a control part 7 which controls a motor 8 for assisting steering which drives a steering wheel, a neutral point detecting circuit 75 detects the neutral point theta0 of the steering angle on the basis of the torque detection signal T, car speed detection signal V, and a revolution detection signal theta, and the difference between the neutral point position theta0 and the revolution position theta of the steering wheel, i.e., the steering angle theta is obtained by an adder 79a. The returned angular speed set value omegaT of the steering wheel is obtained in a function part 76 according to the steering angle theta and the car speed detection signal V, and the difference omega between the returned angular speed set value omegaT and the actual angular speed omegaa is obtained in an adder 79b. The corrected electric current 1a is obtained in a corrected electric current function part 78 on the basis of the difference omega, and the instructed electric current I for the motor 8 is obtained in a function part 72 from the corrected electric current Ia, torque detection signal T, and the car speed detection signal V.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electric power steering device that uses the rotational force of an electric motor to supplement the force required for steering wheel operation.

[Conventional technology]

An electric power steering system installed in a car uses a motor to assist the operating force required to steer the car, and the steering wheel is connected to a steering mechanism in which the steering wheel is interlocked with the steering wheel via a shaft. A torque sensor for detecting the rotational force applied to the steering wheel and a motor for operating the steering mechanism are respectively provided, and the operating force for the steering wheel is reduced by driving the motor in accordance with the detected value of the torque sensor. be.

When returning the steered wheel to the neutral position in the power steering device configured as described above, a torque is generated to return the steered wheel to the neutral position according to the steering angle, and control is performed using this torque to return the steered wheel to the neutral position.

(Problem to be Solved by the Invention) However, in conventional steering wheel return control, since torque is generated to return the steering wheel to the neutral position according to the steering angle, the steering sensation is affected by the speed of the vehicle and the inertia of the motor. is not stable, and the position of the steering wheel may go beyond the neutral position, resulting in a problem of poor steering convergence in the steering wheel return control.

The present invention has been made in view of the above circumstances, and it sets the return angular velocity of the steered wheel according to the steering angle and vehicle speed, and energizes the motor when returning the steered wheel so that the actual angular velocity of the steered wheel matches the set value. It is an object of the present invention to provide a power steering device that prevents excessive steering wheel return control and has good steering convergence by changing the correction current.

[Means for Solving the Problems] A power steering device according to the present invention includes a steering mechanism that converts the rotation of a steering wheel of a vehicle into a left-right movement for steering by applying a steering torque applied to the steering wheel. A power steering device comprising a torque sensor for detection and a steering assist moke for driving the steering wheel according to the detected torque,
a vehicle speed detection means for detecting the vehicle speed of the vehicle; a rudder angle detection means for detecting the rudder angle of the vehicle; and an angular velocity for driving a rudder based on the detection result of the rudder angle detection means and the detection result of the vehicle speed detection means. a steering angular velocity setting means for setting a steering angular velocity setting means, an angular velocity calculating means for calculating an angular velocity for driving the steered wheels from the detection result of the steering angle detecting means, and an angular velocity setting value set by the steering angular velocity setting means and an angular velocity calculating means calculating the angular velocity setting value set by the steering angular velocity setting means. angular velocity deviation calculation means for calculating a deviation from the angular velocity; and when the detected torque is within a predetermined range, the current for driving the motor is controlled based on the calculation result of the angular velocity deviation calculation means; fffl.

[Operation] In the present invention, the steering angular velocity setting value is determined by the steering angular velocity setting means according to the detected steering angle and vehicle speed, and the deviation between this and the angular velocity calculated by the angular velocity calculating means is determined by the angular velocity deviation, To eliminate this angular velocity deviation, the drive current of the motor is controlled according to the angular velocity deviation to drive the steered wheels.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof. Fig. 1 is a partially cutaway front view of the power steering device according to the present invention, Fig. 2 is an enlarged sectional view taken along line 1 and 2 in Fig. 1, and Fig. 3 is the structure of a rotation detector for detecting the steering position. m-m in FIG. v! FIG.

In the figure, 1 is a rack shaft, and a rack shaft case 2 is fixed to a part of the vehicle body and has a cylindrical shape, with the longitudinal direction being the left and right direction.
is interpolated concentrically with this. Reference numeral 3 denotes a pinion shaft, which is supported inside a pinion shaft case 4 connected to one end of the rack shaft case 2 with its axis obliquely intersecting the rack shaft 1 .

The pinion shaft 3 has a torsion bar as shown in FIG.
The upper shaft 3a is supported in the pinion shaft case 4 by a ball bearing 40, and its upper end is connected to the steering wheel via a universal joint (not shown). are linked together. The lower shaft 3b is supported within the pinion shaft case 4 at a position near its upper end by a four-point contact ball bearing 4I, with its lower portion protruding an appropriate length from the lower opening of the pinion shaft case 4. The four-point contact ball bearing 41 is fitted onto the lower shaft 3b from the lower end side, and is fixed by being caulked to the outer peripheral surface of the stepped portion formed near the upper end of the lower shaft 3b. After being positioned on the outside of the lower shaft 3b in the axial length direction with both sides of the inner ring held between the inner ring 42 and the lower shaft 3b, the pinion shaft case 4 is fitted into the pinion shaft case 4 from the lower opening along with the lower shaft 3b. an annular shoulder formed at the bottom of the case 4;
A locking nut 4 is screwed into the case 4 from the opening.
3, the outer ring is held between both sides and positioned inside the pinion shaft case 4 in the longitudinal direction of the shaft, and applies a radial load and a bidirectional thrust load acting on the lower shaft 3b.

Ruhion teeth 30 are formed in the middle part of the lower shaft 3b protruding from the pinion shaft case 4 over an appropriate length in the axial direction. When the rack shaft case 2 is fixed to the upper side of the rack shaft case 2 with the fixing bolt 44, the rack shaft case 2 is fixed to the upper side of the rack shaft case 2. The lower shaft 3b and the rack shaft 1 are engaged with each other with their axes obliquely intersecting each other by meshing with rack teeth 10 formed at a position near one end of the rack shaft 1 over an appropriate length in the shaft length direction. It is combined. The lower shaft 3b extends further downward than the engagement position with the rack shaft 1, and a large bevel gear 31 is fitted to the lower end of the lower shaft coaxially with the lower shaft 3b with its tooth forming surface facing downward. The bevel gear housing 20 is supported by a needle roller bearing 33 in a bevel gear housing 20 that is connected to the lower side of the rack shaft case 2 so as to surround the large cough bevel gear 31. Therefore, the lower shaft 3b is connected to the four-point contact ball bearing 4.
1 and needle roller bearings 33 on both sides of the meshing position between the rack teeth 10 and pinion teeth 30, and the amount of deflection occurring in the lower shaft 3b at the meshing position is kept within a predetermined tolerance range. It will be done.

Furthermore, at the meshing position between the rack teeth 10 and the pinion teeth 30,
A pusher 12 is provided that presses the rank shaft 1 by the biasing force of a push spring 11 toward the pinion shaft 3 so that these are meshed without any gaps. Both radial directions {j
．． It is supported by a bearing pusher 13 that is fitted inside the end of the rack shaft case 2 on the opposite side of the position where it is connected to the pinion shaft case 4, and It is movable internally in the axial direction. Both left and right ends of the rack shaft 1 protruding from both sides of the rack shaft case 2 are connected to separate ball joints 141.
Tie rods 15.4 are connected to the left and right wheels (not shown), respectively. 15, and by moving the rack shaft 1 in the axial direction, the wheels can be steered to the left or right.

Reference numeral 6 in FIG. 2 is a torque sensor that detects the steering torque applied to the steering wheel, and is fitted onto the upper shaft 3a and rotates together with it, and has a lower end face centered on the axis of the upper shaft 3a. a resistor holding member 60 formed of an annular resistor;
A potentiometer is constituted by a detector holding member 61 that is fitted onto the lower shaft 3b and rotates therewith, and has a detector formed on its upper end surface that slides into contact with one point in the radial direction on the resistor. This is what happens. Upper shaft 3a of pinion shaft 3
rotates around its axis in response to the rotation of the steering wheel, but road resistance acting on the wheels acts on the lower shaft 3b via the rack shaft l, and a torsion bar interposed between the two shafts acts on the lower shaft 3b. -5, a twist occurs in accordance with the steering torque applied to the steering wheel. The torque sensor 6 outputs the relative displacement in the circumferential direction that occurs between the upper shaft 3a and the lower shaft 3b due to the torsion of the torsion bar 5 as a potential corresponding to the sliding contact position between the detector and the resistor. The initial M is adjusted so that a predetermined reference potential is output when the torsion bar 5 is not twisted, in other words when the steering wheel is not operated.

The output signal of the torque sensor 6 is input to a control unit 7, and the control unit 7 compares this signal with the reference potential to recognize the direction and magnitude of the steering torque, and is arranged as described below. A drive signal is issued to the motor 8 for steering assistance.

The steering assist motor 8 transmits its rotational force to the lower shaft 3b via an electric clutch 16, a planetary gear reduction device 9, and a small bevel gear 32 with a smaller diameter that meshes with the large bevel gear 31. It is something to do.

The electromagnetic clutch 16 has an annular shape, and is fitted onto one side of the rotating shaft 80 of the motor 8 coaxially with a coil portion 161 fixed to the intermediate case 81 of the motor 8, and rotates together with the rotating shaft 80. and a disc-shaped engaging/disengaging part 163 that faces the main moving part 162 and engages with the main moving part 162 by electromagnetic force caused by energizing the coil part 161. Engages and disengages rotational force.

The planetary gear reduction device 9 is fitted into the engaging/disengaging part 163, rotates, and has a sun gear, one end of which is supported by a bearing fitted into the main moving part, and the other end fitted into a planetary carrier 93, which will be described later. a sun shaft 90 supported on a bearing, and the motor 8
an annular outer ring 91 coaxially fixed to the casing end face 82 of the rotating shaft 80; A plurality of planetary gears 92,92... that rotate around the axis of the sun gear and revolve around the axis of the sun gear, and a planetary carrier 9 that respectively pivotally supports these planetary gears 92,92...
3 and has a smaller outer diameter than the motor 8, and includes the motor 8 and the electromagnetic clutch 1 as an example of the rotating shaft 80.
It is integrated with 6. The output shaft 94 of the 'f1 star gear reduction device 9 is fitted into and fixed to the axial center position of the planetary carrier 93 located coaxially with the rotating shaft 80 of the motor 8, and is projected to the outside of the casing by an appropriate length. The small bevel gear 32 is fitted to the tip of the output shaft 94 with its tooth forming surface facing toward the tip side.
It also rotates in accordance with the revolution of the planetary rollers 92, 92, . . . .

The motor 8, electromagnetic clutch 16, and planetary roller speed reducer 9 are mounted in the bevel gear housing 20 with the small bevel gear 32 inside, with their axes substantially parallel to the axis of the rack shaft l. The small bevel gear 32 is fitted inside the housing 20 and is meshed with the large bevel gear 3l fitted to the lower end of the lower shaft 3b. It is fixed to. The backlash between the large bevel gear 3l and the small bevel gear 32 is adjusted at the butt portion between the casing of the planetary roller reduction gear W9 and the bevel gear housing 20 when the planetary roller reduction gear 9 is fitted into the bevel gear housing 20. This can be easily achieved by changing the thickness and/or number of shims interposed in the shims.

Further, a rotation detector 17 for detecting the rotational position of the motor 8 is provided on the other side of the rotation shaft 80 of the motor 8. A magnet plate 170 having a shape with two N poles and two S poles, and a predetermined mounting angle β (β=135 in this embodiment) around the magnetic plate 170.
) Two reed switches 171 installed without
, 171. FIG. 4 is a waveform diagram showing the output waveform of the rotation detector.

The two reed switches 171.171 have an installation angle β of 1
Since they are mounted at an angle of 35 degrees, the output waveforms are output with a phase shift of 90 degrees. Since this is output in four waveforms each in one rotation, by detecting the rising edge and the falling edge thereof, this rotation detector I7 has a resolution of 1/16 of one rotation.

Compared to conventional rotation detectors such as tachogenerators, this rotation detector 17 can detect rotation speeds starting from 0 and can detect the relative position of the rotor.

In addition, it is smaller than a photointerrupter type rotary encoder, is resistant to high temperatures, and is less susceptible to aging and is cheaper. Furthermore, since the output waveform is a pulse output, the detection results can be easily input into a CPU such as a microcomputer.

In addition to the output signal of the torque sensor 6 mentioned above, the output signal of a rotation detector 17 and the output signal of a vehicle speed detector 18 for detecting vehicle speed are input to the control section 7, and the control section 7 performs the control described later and controls the motor. 8 and the electromagnetic clutch 16 are output.

Next, control by the control section 7 will be explained.

FIG. 5 is a Pronoch diagram showing the configuration and control operation of the control section.

The torque detection signal of the torque sensor 6 advances its phase,
A phase compensation circuit 7I for stabilizing the system and a midpoint detection circuit 75 for determining the midpoint of the steering mechanism are each manually powered.

The vehicle speed detection signal of the vehicle speed detector 18 is generated by an instruction current function unit 72 that generates an instruction current I to the motor 8, which will be described later, and a return angular velocity that sets a target value for the return angular velocity of the steered wheels according to the steering angle Δθ and the vehicle speed. Setting function section 76, midpoint detection circuit 7
5, respectively.

Further, a rotation detection signal θ, which is the rotational position of the motor 8 detected by the rotation detector 17, is manually input to a midpoint detection circuit 75 and an angular velocity detection circuit 77 that detects the angular velocity of rotation of the steering wheel.

The midpoint detection circuit 75 is disclosed in Japanese Patent Application No. 63248 by the inventor of the present application.
This method is similar to that proposed in No. 309, and calculates the midpoint position θ of the steering angle based on the midpoint calculation method described later based on the torque detection signal T, vehicle speed detection signal V, and rotation detection signal. is calculated and the result is given to the adder 79a. The adder 79a calculates the deviation between the rotational position θ of the steering wheel and the midpoint position, that is, the steering angle Δθ, and returns this result to the angular velocity setting function unit 76.

The return angular velocity setting function unit 76 receives the vehicle speed V+ + V21 V. input from the vehicle speed detector 18. The above steering angle Δθ with J... (where v, < v2 < v: I) as a parameter
To? The return angular speed setting value ω■ of the steering wheel is converted into a function, and as the steering angle Δθ becomes smaller, the angular speed setting value ωa becomes smaller, and as the vehicle speed increases, the angular speed setting value ω,
is set to be small.

The return angular velocity setting value ωa of the steered wheel is calculated according to the manually input steering angle Δθ and the vehicle speed input from the vehicle speed detector 18 from the adder 79a, and this result is input to the adder 79b. Further, the angular velocity detection circuit 77 time-differentiates the amount of rotation manually input from the rotation detector 17 to obtain the angular velocity ω1 during steering of the steering wheel, and inputs this result to the adder 79b.

In the adder 79b, the manually input return angular velocity set value ω
Find the angular velocity deviation Δω=ω7ω1 between A and angular velocity ω1,
This result is input to the correction current function section 78. In the correction current function unit 78, the angular velocity deviation Δω and the correction current I. The relationship between the input angular velocity deviation Δω is preset as a function, and the input angular velocity deviation Δω is subjected to a PID calculation, and a correction current corresponding to the calculation result is obtained, and this result is manually input to the I indication current function section 72. .

The command current function section 72 receives the torque T which is the output signal of the phase compensation circuit 71, the vehicle speed detection signal V given by the vehicle speed detector 18, and the correction current 1 from the correction current function section 78, respectively. The instruction current function section 72 receives the vehicle speed detection signal V.
The relationship between the instruction current 1 to the motor 8 and the torque T with the correction current I and I as parameters is set as a function in advance, and the instruction to the motor 8 is determined by the torque T which is the output signal of the phase compensation circuit 71. Calculate the voltage IA I and input the result to the adder 79c.

The adder 79c receives the command current I and the feed hack signal from the current detection circuit 74 that detects the current consumption of the mork 8, and calculates the deviation between them. This result is calculated using PWM (Pulse-Width Modulation).
n: pulse width modulation) is applied to the motor 8 via the drive circuit 73.

Next, the calculation of the midpoint of the steering wheel in the control section 7 as described above and the return control of the steering wheel, which is the gist of the present invention, will be explained.

FIG. 6 shows the indicated current I and torque T in the indicated current function section 72.
This is a graph showing the characteristics of the relationship between the command current I and the vertical axis.
, and the torque T is plotted on the horizontal axis. The positive side of the torque T on the horizontal axis indicates the torque for right steering, and the negative side indicates the torque for left steering. Further, the positive side of the instruction current I indicates a current that causes the motor 8 to rotate to the left, and the negative side indicates a current that causes the motor 8 to rotate to the right.

Furthermore, the dashed line indicates vehicle speed V+, Vz + v3...
The broken line indicates the steering angular velocity deviation Δ
It shows the instruction current I to the motor 8 when the steering wheel is returned, which is changed by the correction current (3) when the steering wheel is returned, which is determined by ω.

In addition, D1 and D2 indicate a dead zone, and when the steering torque to the right (or left) due to a steering operation exceeds the range within the dead zone D1 to D2, the instruction current I of the motor 8 increases as the torque T increases. However, the steering assist force by the motor 8 increases. In this case, the relationship between torque T and command current I is vehicle speed v, + v2 *V=・−・(however, V+ < v2
<vl) and vehicle speed? As the speed increases, the torque T
The instruction current I for the current is increased.

In this way, when operating the steering wheel to the right (or left) and then returning the steering wheel, if the torque T falls within the dead zone D, ~D2, the correction voltage i+■ (or I.) shown by the broken line will increase. The indicated current becomes I, and then the torque T becomes the dead zone D.
If it is within z, the indicated current 1 is equal to this correction current -1. (or!), and the motor 8 is driven with a constant torque. As a result, the steering assist force when returning the steering wheel becomes constant.

This correction current 1. The absolute value of the actual steering wheel angular velocity ω increases as the steering angular velocity deviation Δω increases. When the deviation from the return angular velocity set value ω7 is large, the command current (2) is increased to increase the control speed.

FIG. 7 is a flowchart showing a method of calculating the midpoint of the steering wheel. In step 1, the vehicle speed V is read, and in step 2, it is determined whether the vehicle speed V is larger than a threshold value v5■. If it is larger, the vehicle speed is determined in step 3. ? Torque setting according to {ii
Determine T s z and then in step 4
In step 5, it is determined whether the torque torque T is smaller than the torque setting value Ts2. If it is small, it is determined that the vehicle is moving straight, and in step 6 the number of times the small is small is counted, and in step 7 the motor 8 at that time is
Read the rotation position of. Then, in step 8, the rotational position is added to the total rotational position up to the previous time, the addition result is divided by the number of counts to obtain the steering angle midpoint, and the value of the steering angle midpoint is updated. Further, if the vehicle speed V is smaller than the threshold value ■8■ in step 2, or if the torque T is larger than the torque setting value 'Lz in step 5, the process returns.

FIG. 8 is a flowchart showing steering wheel return control;
The operation of the signal path from the adder 79a to the adder 79c in FIG. 5 is shown. In the steering wheel return control, the midpoint position θ obtained as described above is determined in step 9. is read, and in step 10, the steering wheel position θ is read. Then adder 79a
, the center point position θ is determined from the steering wheel position θ. The steering angle Δθ is determined by subtracting (step 11).

In step 12, the return angular speed setting function unit 76 determines the return angular speed setting value ω7 of the steered wheel based on the steering angle Δθ and the vehicle speed V. On the other hand, the angular velocity detection circuit 77 differentiates the rotation amount inputted from the rotation detector 17 with respect to time to obtain the actual steering angular velocity ω7 (step 13). Step I4
, the adder 79b calculates the return angular velocity setting value ω
The steering angular velocity deviation Δω is calculated by subtracting the steering angular velocity ω1 from A. Next, in step 15, the correction current function unit 7
After PID calculation of the steering angular velocity Δω is performed in step 8, this is calculated using a predetermined steering angular velocity Δω and a correction current 1. It is converted into a correction current I1 based on the relationship with . Then, in step 16, the instruction current function unit 72 generates a correction current ① as shown in FIG. Change settings.

Then, an instruction current l is determined based on the torque T, the vehicle speed V, /%-V3..., and the correction current I.

When the value of torque T is within the dead zone DI' = D2 and the vehicle speed is fast (V,), the ratio of increase in the indicated current I to torque T is made smaller than when the vehicle speed is slow (V3). , and when the torque T is within the unfavorable zone D1 to D2, the instruction current I is the correction current I. as described above. is controlled to a constant value. This correction current I1 is set to increase as the steering angular velocity deviation Δω increases, and the correction current I1 is set to increase as the steering angular velocity deviation Δω increases. The tracking performance for the return angular velocity setting value ω is improved. By performing the above control, a stable steering feeling can be obtained near the midpoint of the steering angle when the steering wheel is returned.

By controlling the steering angular velocity in accordance with the steering angle and the vehicle speed in this manner, it is possible to prevent the vehicle from going too far past the midpoint of the steered wheels, allowing stable steering.

[Effects] As detailed above, in the power steering system according to the present invention, the return angular velocity of the steered wheel is set according to the steering angle and vehicle speed, and the return angular velocity of the steered wheel is adjusted to the motor so that the actual angular velocity of the steered wheel matches this setting. By controlling the current to be applied, the present invention has excellent effects such as preventing excessive return control of the steering wheel and improving steering convergence.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view showing an embodiment of a power steering device according to the present invention, FIG. 2 is an enlarged sectional view taken along the line n-tt in FIG. 1, and FIG. 3 is a structure of a rotation detector. FIG. 4 is a waveform diagram showing the output waveform of the rotation detector; FIG. 5 is a block diagram showing the configuration and operation of the control section; FIG. 8 is a flow chart explaining each control operation, and FIG. 6 is a graph showing the characteristics of the relationship between motor current and torque in the command current function section. 6... Torque sensor 8... Motor 17... Rotation detector 18... Vehicle speed detector 75... Midpoint detection circuit 71d... Rudder angle determination circuit patent Applicant: Koyo Seiko Co., Ltd. agent People Patent Attorney Noboru Kono Diagram Diagram Genkomu's Condolence Diagram Condolence Diagram His Brother's Diagram

Claims (1)

[Scope of Claims] 1. A steering mechanism that converts the rotation of a steering wheel of a vehicle into a left-right movement for steering, includes a torque sensor that detects a steering torque applied to the steering wheel, and a torque sensor that responds to the detected torque. A power steering device comprising a steering assist motor for driving the steering wheel, comprising: a vehicle speed detecting means for detecting a vehicle speed of the vehicle; a steering angle detecting means for detecting a steering angle of the vehicle; Steering angular velocity setting means for setting an angular velocity for driving the steered wheels based on the detection results of the steering angle detection means and the detection results of the vehicle speed detection means; and angular velocity calculation for calculating the angular velocity for driving the steered wheels from the detection results of the steering angle detection means. means, angular velocity deviation calculation means for calculating the deviation between the angular velocity setting value set by the steering angular velocity setting means and the angular velocity calculated by the angular velocity calculation means, and when the detected torque is within a predetermined range, the angular velocity deviation calculation means A power steering device comprising: means for controlling a current for driving the motor based on a calculation result.