JPH0775986B2 - Power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric power steering apparatus (power steering) that assists a force required for operating a steering wheel with a rotational force of a motor.

[Prior art]

The steering torque applied to the steered wheels is detected, and when the detected torque exceeds a predetermined dead zone, a drive current proportional to the detected torque is caused to flow through a motor for steering assistance to drive the motor, and An electric power steering apparatus has been developed in which a force required for steering is assisted by a rotational force of the motor to provide a driver with a comfortable steering feeling.

In such a power steering apparatus, when the steering assist force during high-speed traveling is large, there is a problem in that the steering feeling feels unstable and the steering feeling is unnatural due to the inertial force of the motor. Then, in order to solve the above-mentioned problem, the steering assist force is reduced by subtracting a value proportional to the angular velocity of the steering wheel rotation and the vehicle speed from the target value of the drive current passed through the motor, and the steering feeling is reduced. The feeling of wobbling and unnaturalness were suppressed.

This control uniformly reduces the output torque obtained by adding the steering assist force to the input torque applied to the steering wheel, regardless of the magnitude of the input torque. That is, the input torque required to obtain a predetermined output torque is increased.

[Problems to be Solved by the Invention]

However, in the conventional power steering apparatus as described above, the relationship between the input torque and the output torque is that the input torque and the output torque are equal in the dead zone because the steering assist force is not applied to the input torque, and Outside the dead zone, the steering assist force is applied to the input torque, so that the ratio of the output torque to the input torque is larger than that in the dead zone. Therefore, when the above control is performed, the increase amount of the input torque required to obtain the predetermined output torque is smaller when the input torque is outside the dead zone than when the input torque is inside the dead zone. As described above, since the increase amount of the input torque is different inside and outside the dead zone, there is a problem that the braking effect by the control becomes discontinuous and the steering feeling becomes discontinuous.

The present invention has been made in view of such circumstances, and is determined separately from the detected value of the torque applied to the steering wheel and the target value of the motor current for steering assistance, depending on the angular velocity of the steering wheel rotation and the vehicle speed. An object of the present invention is to provide a power steering apparatus that suppresses discontinuity of steering feeling by subtracting a value.

[Means for Solving the Problems]

The power steering apparatus according to the present invention includes an angular velocity detecting means for detecting an angular velocity of a steering wheel, a vehicle speed detecting means for detecting a vehicle speed, a torque sensor for detecting a steering torque applied to the steering wheel, and a detected steering torque. A power steering apparatus including a steering assisting motor driven by a corresponding current, wherein a value corresponding to each detection result of the angular velocity detecting means and the vehicle speed detecting means is subtracted from the detected steering torque. And a means for subtracting a value corresponding to the detection result of each of the angular velocity detection means and the vehicle speed detection means from the current.

[Action]

For each of the steering torque detection result and the motor driving current determined according to the outside detection result, the angular velocity detection means and the vehicle speed detection means are individually set to be large as the detection results become large. The obtained values are subtracted from the detection result of the steering torque and the current.

This increases the steering torque required for a predetermined steering amount and suppresses the feeling of swaying during high-speed running.However, if a predetermined value is subtracted from the current, the steering amount required for steering assist is required. The amount of increase in steering torque is smaller than the amount of increase in steering torque during non-steering assistance. So
In order to reduce the difference in the steering torque increase amount between the steering assist time and the non-steering assist time, subtraction of the steering torque detection result is performed to increase only the steering torque required for the predetermined steering amount during the steering assist. To do. As a result, it is possible to suppress the discontinuity of steering during high-speed traveling.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof. 1 is a partially cutaway front view of a power steering apparatus according to the present invention, FIG. 2 is an enlarged sectional view taken along line II-II of FIG. 1, and FIG.
The drawing is an enlarged sectional view taken along the line III-III in FIG. 1 showing the structure of the rotation detector.

In the figure, reference numeral 1 denotes a rack shaft, and a rack shaft case 2 which is fixed to a part of the vehicle body and has a cylindrical shape with the longitudinal direction being the left-right direction.
It is interpolated concentrically with this. Further, 3 is a pinion shaft, which is rotatably supported inside the pinion shaft case 4 continuously provided in the vicinity of one end of the rack shaft case 2 in a state in which its axis is oblique to the rack shaft 1.

As shown in FIG. 2, the pinion shaft 3 is composed of an upper shaft 3a and a lower shaft 3b which are coaxially connected to each other via a torsion bar 5, and the upper shaft 3a is installed in a pinion shaft case 4 by a ball bearing 40. It is supported and its upper end is interlocked with the steering wheel via a universal joint (not shown). The lower shaft 3b is supported in the pinion shaft case 4 by a four-point contact ball bearing 41 at a position near the upper end of the lower shaft 3b with the lower portion thereof appropriately protruding 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 thereof,
A step portion formed in the vicinity of the upper end portion of the lower shaft 3b, and a collar 42 fixed by caulking to the outer peripheral surface fitted from the lower end portion side are clamped on both sides of the inner ring so that the shaft is provided outside the lower shaft 3b. After being positioned in the longitudinal direction, the lower shaft 3b is fitted into the pinion shaft case 4 through the lower opening, and an annular shoulder is formed in the lower portion of the outer case 4, and the outer case 4 is screwed through the opening. With the combined lock nut 43, both sides of the outer ring are clamped and positioned in the pinion shaft case 4 in the axial direction, and a radial load acting on the lower shaft 3b and a thrust load in both directions are applied.

In the middle of the lower shaft 3b protruding from the pinion shaft case 4, there are formed pinion teeth 30 having an appropriate length in the axial direction thereof. When fixed to the upper side of the rack shaft case 2 with a fixing bolt 44, a rack formed inside the rack shaft case 2 at a position near one end of the rack shaft 1 over a suitable length in the axial direction. The lower shaft 3b and the rack shaft 1 are meshed with the teeth 10 and are engaged with each other with their axes intersecting each other. The lower shaft 3b extends further downward than the engagement position with the rack shaft 1, and has a lower end portion coaxial with the lower shaft 3b, and a large bevel gear 31 is fitted with its tooth forming surface facing downward. The large bevel gear 31 is supported by a needle roller bearing 33 in a bevel gear housing 20 that is continuously provided below the rack shaft case 2 in a manner surrounding the large bevel gear 31. Therefore, the lower shaft 3b has a rack tooth by the four-point contact ball bearing 41 and the needle bearing 33.
It is supported on both sides of the meshing position between the 10 and the pinion teeth 30, and the amount of bending of the lower shaft 3b at the meshing position is kept within a predetermined allowable plate.

Further, at the meshing position of the rack tooth 10 and the pinion tooth 30, a pusher for pushing the rack shaft 1 by the urging force of the push spring 11 toward the pinion shaft 3 so that they are meshed without a gap.
12 is provided, the rack shaft 1 is supported by the pressing element 12 and the lower shaft 3b at both sides in the radial direction at the meshing position, and the rack shaft 1 is opposite to the continuous position with the pinion shaft case 4. Is supported by a bearing bush 13 fitted in the end portion of the rack shaft case 2 on the side, and is movable in the axial direction thereof inside the rack shaft case 2. The left and right ends of the rack shaft 1 protruding from both sides of the rack shaft case 2 are connected to tie rods 15 and 15 connected to left and right wheels (not shown) via separate ball joints 14 and 14, respectively. The wheels are steered to the left and right by the movement of the rack shaft 1 in the axial direction.

Reference numeral 6 in FIG. 2 is a torque sensor for detecting the steering torque applied to the steering wheel, which is externally fitted to the upper shaft 3a and rotates together therewith, and the lower end face of the torque sensor is centered on the shaft center of the upper shaft 3a. And a resistor holding member 60 formed of an annular resistor, and a detector externally fitted to the lower shaft 3b and rotated together with the lower shaft 3b and slidingly contacting the upper end face of the resistor in a radial direction on the resistor. A potentiometer is configured with the detector holding member 61 formed by. The upper shaft 3a of the pinion shaft 3 rotates about its axis according to the rotation of the steering wheel, but the road surface resistance acting on the wheels acts on the lower shaft 3b via the rack shaft 1,
The torsion bar 5 interposed between the two shafts is twisted according to the steering torque applied to the steering wheel. Torque sensor 6
Is the upper shaft 3a and the lower shaft 3b as the torsion bar 5 is twisted.
The relative displacement in the circumferential direction generated between and is output as a potential corresponding to the sliding contact position between the detection element and the resistor. When the torsion bar 5 is not twisted, in other words, steering wheel operation is performed. The initial adjustment is made so as to output a predetermined reference potential when not performed. Torque sensor 6
Is output to the control unit 7 in time series, and the control unit 7 compares the signal with the reference potential to recognize the direction and the magnitude of the steering torque, and is arranged as described later. A drive signal is issued to the steering assisting motor 8.

The steering assisting motor 8 transmits its rotational force to the lower shaft 3b via an electromagnetic clutch 16, a planetary gear speed reducer 9 and a small bevel gear 32 that meshes with the large bevel gear 31 and has a smaller diameter than this. Is.

The electromagnetic clutch 16 has an annular shape and is an intermediate case of the motor 8.
A coil portion 161 fixed to 81, a main driving portion 162 which is fitted onto one side of the rotation shaft 80 of the motor 8 coaxially therewith, and rotates together with the rotation shaft 80, and a disk-shaped main driving portion 162. It is opposed to 162 and is driven by the electromagnetic force generated by energizing coil section 161.
The motor 8
Is engaged and disengaged.

The planetary gear speed reducer 9 is fitted in the engagement / disengagement portion 163, rotates, and has a sun gear. One end of the planetary gear reduction gear 9 is supported by a bearing fitted in the main drive portion, and the other end is fitted in a planet carrier 93 described later. A sun shaft 90 supported by a fixed bearing, a ring-shaped outer ring 91 fixed to a casing end surface 82 of the motor 8 coaxially with the rotating shaft 80, an inner peripheral surface of the outer ring 91 and the Sun axis 90
A plurality of planet gears 92, 92 that rotate around the sun gear's outer peripheral surface, respectively, rotate about their respective axes and revolve around the axis of the sun gear, and these planet gears 92, 92, respectively. It is composed of a planet carrier 93 which is axially supported, has an outer diameter smaller than that of the motor 8, and is integrated with the motor 8 and the electromagnetic clutch 16 on one side of the rotating shaft 80. The output shaft 94 of the planetary gear reduction device 9 is fitted and fixed in the axial center position of the planet carrier 93 located coaxially with the rotation shaft 80 of the motor 8, and is projected to an appropriate length outside the casing. The bevel gear 32 is fitted to the tip of the output shaft 94 with its tooth forming surface facing the tip. The bevel gear 32 together with the output shaft 94 is connected to the planet gears 92, 92 ... It is designed to rotate according to the revolution of the.

The motor 8, the electromagnetic clutch 16, and the planetary gear speed reducer 9 are installed in the bevel gear housing 20 with the small bevel gear 32 inside while the axes thereof are substantially parallel to the axis of the clutch shaft 1. The large bevel gear in which the small bevel gear 32 is fitted inside the housing 20 and is fitted to the lower end of the lower shaft 3b.
It is engaged with 31 and is fixed to a bracket 2a provided outside the rack shaft case 2. Backlash adjustment between the large bevel gear 31 and the small bevel gear 32 is performed by fitting the casing of the planetary gear reduction device 9 and the bevel gear housing 20 together when the planetary gear reduction device 9 is fitted into the bevel gear housing 20. It can be easily carried out by changing the thickness and / or the number of the systems to be inserted in.

Further, a rotation detector 17 for detecting the rotation position of the motor 8 is provided on the other side of the rotation shaft 80 of the motor 8, and the rotation detector 17 is a disc externally fitted on the other side of the rotation shaft 80 of the motor 8. Make a state,
It is composed of a magnet plate 170 having two north and south poles, and two reed switches 171 and 171 mounted around the magnet plate 170 with a predetermined mounting angle β (β = 135 ° in this embodiment).
FIG. 4 is a waveform diagram showing the output waveform of the rotation detector. Two
Since the two reed switches 171, 171 are mounted without mounting angle β of 135 °, the output waveforms are output with a 90 ° phase shift. Since each of these outputs four waveforms in one rotation, the rotation detector 17 has a valve resolution of 1/16 of one rotation by detecting the rising and falling edges.

The rotation detector 17 can detect the rotation speed from 0 and can detect the relative position of the rotor, as compared with a conventional rotation detector such as a tachogenerator.

In addition, it is smaller than the photo interrupter type rotary encoder, is resistant to high temperatures, is less subject to aging, and is less expensive. Furthermore, since the output waveform is a pulse output, the detection result can be easily loaded into a CPU such as a microcomputer.

Further, in addition to the output signal of the torque sensor 6 described above, the output signal of the rotation detector 17 and the output signal of the vehicle speed detector 18 for detecting the vehicle speed are input to the control unit 7, and the control described below is performed. A drive signal for driving the motor 8 is output.

Next, the control by the control unit 7 will be described.

FIG. 5 is a block diagram showing the configuration and control operation of the control unit.

The torque detection signal of the torque sensor 6 advances its phase,
It is given to the phase compensating circuit 71a for stabilizing the system, phase-compensated by the phase compensating circuit 71a, and given to the subtractor 74a as the compensation detection torque Tc. Further, the vehicle speed detection signal of the vehicle speed detector 18 is a command current I of the motor 8 described later.
To a subtraction signal function unit 73a for generating a subtraction signal Sr for subtracting the values of the torque detection signal and the instruction current I. Then, the rotation detection signal of the rotation detector 17 is given to the angular velocity detection circuit 71b, is differentiated by the angular velocity detection circuit 71b, and is given to the subtraction signal function unit 73b as the angular velocity ω.

In the subtraction signal function unit 73b, the relationship between the angular velocity ω and the subtraction signal Sr is functionalized according to the value of the vehicle speed V,
A subtraction signal Sr is obtained from the angular velocity ω and the vehicle speed V, and the subtraction signal Sr is used as the first gain compensation circuit 75a and the second gain compensation circuit 75b.
Given to. In the first gain compensation circuit 75a, the subtraction torque Tr to be subtracted from the compensation detection torque Tc is calculated by multiplying the input subtraction signal Sr by a predetermined value, and the calculation result is given to the subtractor 74a.

In the subtractor 74a, the subtraction torque Tr is subtracted from the input compensation detection torque Tc, and the subtraction result is given as the input torque T to the instruction current function unit 73a. In the command current function unit 73a, the relationship between the input torque T and the command current I is functionalized according to the value of the vehicle speed V. The command current I is obtained from the input torque T and the vehicle speed V, and the command current I Is supplied to the subtractor 74b.

In the second gain compensation circuit 75b, a subtraction current Ir to be subtracted from the instruction current I is calculated by multiplying the input subtraction signal Sr by a predetermined value, and the calculation result is the subtractor.
Given to 74b.

The subtractor 74b performs an operation of subtracting the subtraction current Ir from the input current I input, and the subtraction result is given to the subtractor 74c.

In the subtractor 74c, a current detection resistor (not shown) is inserted in the motor line from the subtraction result, the feedback signal from the current detection circuit 71c that detects the consumption current of the motor 8 is reduced, and the subtraction result is PWM (pulse−Width
Modulation (pulse width modulation) is given to the motor 8 via a drive circuit 72. The current detection circuit 71c is configured to detect the current including the flywheel current of the motor, and the current loop is stable.

Next, the operation will be described.

FIG. 6 is a flowchart showing a procedure of control for reducing the steering assist force according to the vehicle speed and the rotation speed of the steered wheels.

First, in step 1, torque sensor 6, rotation detector
The torque detection signal, the rotation speed of the steering wheel, and the vehicle speed V are read from the vehicle speed detector 17 and the vehicle speed detector 18, respectively.

Next, the phase compensation circuit 71a converts the torque detection signal into the compensation detection torque Tc, and the angular velocity detection circuit 71b calculates the angular velocity ω of the rotation of the steered wheels from the rotational speed of the steered wheels (step 2). Then, in step 3, the subtraction signal Sr is calculated from the vehicle speed V and the angular velocity ω input in the subtraction signal function unit 73b and output to the first gain compensation circuit 75a and the second gain compensation circuit 75b.

FIG. 7 is a graph showing the characteristic of the relationship between the subtraction signal Sr and the angular velocity ω in the subtraction signal function unit 73b. The subtraction signal Sr increases in proportion to the increase of the angular velocity ω, and this proportional relationship shows the vehicle speed.
Depending on V ₁ , V ₂ , V ₃ (V ₁ <V ₂ <V ₃ ), the ratio of the subtraction signal Sr to the input angular velocity ω becomes larger as the vehicle speed V becomes faster. Therefore, the subtraction signal Sr increases as the vehicle speed V and the angular velocity ω increase.
Then, the first gain compensation circuit 75a multiplies the subtraction signal Sr by a predetermined value to obtain the subtraction torque Tr, and the second gain compensation circuit 75b multiplies the subtraction signal Sr by a predetermined value to obtain the subtraction current Ir.

Next, in step 4, the compensation detection torque T is calculated in the subtractor 74a.
The subtraction torque Tr is subtracted from c to obtain the input torque T.

In step 5, the command current function unit 73a generates the command current I of the motor 8 from the input torque T and the vehicle speed V.
FIG. 8 shows a method of determining the instruction current I.

FIG. 8 is a graph showing the characteristic of the relationship between the instruction current I and the input torque T in the instruction current function unit 73a, where the vertical axis is the instruction current I and the horizontal axis is the input torque T. The positive side of the input torque T on the horizontal axis is the input torque T in the case of right steering.
The negative side shows the input torque T for left steering. Further, the positive side of the instruction current I indicates a current that causes the motor 8 to rotate to the right, and the negative side indicates a current that causes the motor to rotate to the left. Further, the alternate long and short dash line shows the above characteristics which differ depending on the vehicle speeds V ₁ , V ₂ , V ₃ ...

Further, -D to D represent dead zones, and the input torque T for steering to the right (or left) by steering wheel operation is the dead zone -D to D.
When the value exceeds the range, the instruction current I of the motor 8 increases as the input torque T increases, and the steering assist force of the motor 8 increases. In this case, the instruction current I increases until the input torque T reaches the low torque set value −Ts to Ts, regardless of the input vehicle speed V, and when it exceeds this, the relationship between the input torque T and the instruction current I becomes large. Vehicle speed V ₁ , V ₂ , V ₃ … (However, V ₁ <V ₂ <
V ₃ ), the input torque T increases as the vehicle speed increases.
The instruction current I for is small.

Then, in step 6, the subtractor 74b subtracts the subtraction current Ir from the instruction current I. Then, the motor 8 is driven by the instruction current I after the subtraction (step 7).
The subtraction of the subtraction current Ir from the instruction current I means that when the input torque T is in the dead zone in the instruction current function unit 73a, it is smaller than when the input torque T is outside the dead zone.
This is effective in increasing the amount of increase in steering torque. This is because the steering assist is not performed within the dead zone, and the ratio of the output torque, which is the torque actually applied to the steering device, to the input torque T, which is the torque due to the steering wheel operation, is smaller than that outside the dead zone. This is because the subtraction effect of is large. However, the subtraction effect in the dead zone is larger than that in the dead zone only by subtraction of the instruction current I, and a discontinuous steering feeling is felt. Therefore, the subtraction torque Tr is subtracted from the compensation detection torque Tc on the upstream side of the instruction current function unit 73a. By subtracting, the subtraction effect outside the dead zone is increased and the amount of increase in steering torque is increased. This is because if the compensation detection torque Tc is subtracted before the instruction current I is generated, if the input torque T is within the dead zone, the instruction current is zero, so there is no subtraction effect on the instruction current, and the input torque T does not reach the dead zone. This is because it is effective only when it is outside.

Thus, with respect to the increase in the steering torque, the subtraction current Ir is effective when the input torque T is within the dead zone, while the subtraction torque Tr is effective when the input torque T is outside the dead zone. Gain compensation circuit 75a and second gain compensation circuit 7
By adjusting the respective gains of 5b, it is possible to suppress the discontinuity in the subtraction control of the output torque during high-speed traveling.

〔effect〕

As described above in detail, in the power steering apparatus according to the present invention, the detected value of the torque applied to the steered wheels and the target value of the motor current for steering assistance are individually determined according to the angular velocity of the steered wheel rotation and the vehicle speed. The present invention has an excellent effect such that a feeling of discontinuity in steering during high-speed traveling can be suppressed by subtracting the value that is set.

[Brief description of drawings]

1 is a partially cutaway front view showing an embodiment of a power steering apparatus according to the present invention, FIG. 2 is an enlarged sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a structure of a rotation detector. III-I in FIG.
Fig. 4 is an enlarged sectional view taken along line II, 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 unit, and Fig. 6 is the traveling speed and rotation speed of the steering wheel. FIG. 7 is a flowchart showing the procedure of control for reducing the steering assist force in accordance with the graph, FIG. 7 is a graph showing the characteristic of the relationship between the subtraction signal in the subtraction signal function part and the angular velocity, and FIG. 6 is a graph showing the characteristic of the relationship between the input torque and the input torque. 6 ... Torque sensor, 8 ... Motor 17 ... Rotation detector, 18 ... Vehicle speed detector 71b ... Angular velocity detection circuit, 73a ... Indication current function part 73b ... Subtraction signal function part, 75a ... 1st Gain compensation circuit 75b ... Second gain compensation circuit

Claims (1)

[Claims] 1. An angular velocity detecting means for detecting an angular velocity of a steering wheel, a vehicle speed detecting means for detecting a vehicle speed, a torque sensor for detecting a steering torque applied to the steering wheel, and a current according to the detected steering torque. A power steering apparatus including a steering assisting motor, wherein a value corresponding to each detection result of the angular velocity detecting means and the vehicle speed detecting means, means for subtracting from the detected steering torque, A means for subtracting a value corresponding to the detection result of each of the angular velocity detecting means and the vehicle speed detecting means from the current, the power steering apparatus.