JP2000118425A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor-driven power steering device provided with an excellent steering wheel return property even at a low and high friction factor road and improved in an steering wheel return property in particular on a low friction factor road. SOLUTION: A steering control device 19 is provided with a central processing device (CPU) 20, An ECU 18 for an ABS(Antilock Brake System) calculates a road friction factor μ and inputs it to a CPU 18. The CPU 20 computes a steering wheel rotation angular speed ω based on a motor current Im and a voltage Vm between motor terminals. A current output value to a motor 7 is increased so that during low speed running, on the low μ road side where the road friction factor μ is low, a steering wheel return force is increased to a value higher than that on the high μ road side wherein the road friction factor μ is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for a vehicle, and more particularly to an electric power steering device.

[0002]

2. Description of the Related Art Conventionally, an electric power steering device (electric power steering device) for a vehicle detects a steering torque generated on a steering shaft by operating a steering wheel, and based on the detected signal, detects a motor torque. A current command value which is a control target value is calculated. And
In a current feedback control circuit, a difference between a current command value, which is a control target value, and a current actually flowing through the motor is obtained as a current control value, and the motor is controlled by the current control value to control a steering force of a steering wheel. Is assisting.

[0003] Generally, a steering steering mechanism operates by rotating a steering handle during running, and then, when the steering handle is released from the steering handle, a self-aligning torque due to a reaction force from a road surface (tire). As a result, the vehicle automatically returns to the straight traveling position (neutral position).

In the electric power steering apparatus, the steering mechanism is rotated when the steering wheel is rotated during traveling as described above, and then, when the steering wheel is released (hereinafter, referred to as handle return), the steering mechanism is operated. The driving motor has inertia. Due to the inertia of the motor, the return of the steering wheel is poor during low-speed traveling, and the vibration occurs to swing to the opposite side beyond the neutral position during high-speed traveling.

[0005] In order to prevent such a situation, a conventional electric power steering apparatus controls the steering handle to return easily during low-speed running and to suppress vibration of the steering mechanism during high-speed running (hereinafter referred to as steering wheel return control). ) Is done.

[0006] Conventionally, when the electric power steering apparatus is commercialized so as to be capable of performing the above-described steering wheel return control, the electric power steering apparatus normally travels on a dry road (hereinafter referred to as a high μ road). Tunes various parameters required for steering wheel return control and evaluates feeling.

[0007]

However, in a vehicle equipped with an electric power steering device employing various parameters obtained on a high μ road as described above, for example, a fresh snow road, a compact snow road or a frozen road in a cold region ( Traveling on a low μ road) has the following problems.

That is, since the friction coefficient μ between the low μ road surface and the tire is smaller than the friction coefficient μ on the high μ road (dry road) surface, the reaction force from the road surface becomes small. For this reason, since the reaction force from the road surface is reduced, there is a problem that the steering wheel returnability after steering the steering wheel is deteriorated, especially during low-speed running.

An object of the present invention is to provide an electric power steering apparatus which can obtain a good steering wheel return property on both a low μ road and a high μ road, and in particular, has a good steering wheel return property on a low μ road. It is in.

[0010]

According to a first aspect of the present invention, a steering wheel return force is calculated on the basis of at least a steering wheel angular velocity generated by operating a steering shaft and a vehicle speed, and based on the calculation result. In an electric power steering apparatus including a control unit that controls an output of a motor that applies a steering wheel return force to a steering mechanism, a friction coefficient estimation unit that estimates a road surface friction coefficient of a traveling road during traveling, the control unit includes: According to the road coefficient of friction estimated by the friction coefficient estimating means, the current output to the motor is increased on the low μ road side where the road friction coefficient is low as compared with the high μ road side where the road friction coefficient is high, so as to increase the steering wheel return force. The gist of the present invention is an electric power steering device for increasing the value.

According to a second aspect of the present invention, a steering wheel return force is calculated based on at least a steering wheel angular velocity generated due to operation of a steering shaft and a vehicle speed, and the steering mechanism is provided with a steering wheel return force based on the calculation result. An electric power steering apparatus comprising a control means for controlling an output of a motor that imparts a coefficient of friction, wherein a friction coefficient estimating means for estimating a road surface friction coefficient of a running road at the time of traveling is provided, and the control means reduces a friction coefficient to a magnitude. A plurality of steering wheel return maps in accordance with the road surface friction coefficient estimated by the friction coefficient estimating means based on the steering wheel return map. The gist of the present invention is an electric power steering device that increases a current output value to a motor so as to increase a steering wheel return force as compared with a road side. It is.

[0012] The invention of claim 3 is claim 1 or claim 2.
, A gist of the present invention relates to an electric power steering apparatus provided with detection means for detecting a steering wheel angular velocity generated due to operation of a steering shaft.

According to a fourth aspect of the present invention, there is provided the first to third aspects.
In any one of the above, the control means calculates a μ-sensitive gain based on a μ-sensitive gain map that obtains a μ-sensitive gain from the road surface friction coefficient estimated by the friction coefficient estimating means, and uses the steering wheel rotation angular velocity at that time. Then, a high-μ road basic steering wheel return current is calculated based on the vehicle speed-sensitive steering wheel return map on the high μ road, and the low-road road-sensitive steering wheel return map on the low μ road is used by using the steering wheel angular velocity at that time. An electric power steering device that calculates a μ-road basic steering wheel return current, calculates the steering wheel return current by interpolation calculation using the μ-sensitive gain, and controls the motor with the obtained steering wheel return current. It is the gist.

According to a fifth aspect of the present invention, there is provided the first to third aspects.
In any one of the above, the control means uses a plurality of vehicle speed sensitive steering wheel return maps created in advance for each of a plurality of road surface friction coefficients divided into a plurality of ranges, and the friction coefficient estimating means estimates from the map. An electric power steering apparatus comprising: a steering wheel return map selecting means for selecting a map corresponding to a road surface friction coefficient; calculating a steering wheel return current from the selected steering wheel return map; and controlling a motor with the obtained steering wheel return current. It is the gist.

(Operation) According to the first aspect of the present invention,
The friction coefficient estimating means estimates a road surface friction coefficient of the traveling road during traveling. The control means, according to the road surface friction coefficient estimated by the friction coefficient estimation means, on the low μ road side where the road surface friction coefficient is low,
The current output value to the motor is increased so as to increase the steering wheel return force at the time of low-speed running compared with the high μ road side having a high road friction coefficient. As a result, on a low μ road, a high μ
Gives a larger steering wheel return force to the steering mechanism than to the road.

According to the second aspect of the present invention, the friction coefficient estimating means estimates the road surface friction coefficient of the road during traveling.
The control means has a plurality of steering wheel return maps according to the magnitude of the friction coefficient, and based on the steering wheel return maps, according to the road surface friction coefficient estimated by the friction coefficient estimating means, the road surface friction coefficient is low and low μ. On the road side, the current output value to the motor is increased so as to increase the steering wheel return force as compared with the high μ road side having a high road friction coefficient.

According to the third aspect of the present invention, the first aspect is provided.
Alternatively, in addition to the function of the second aspect, the detecting means detects a steering wheel angular velocity generated due to the operation of the steering shaft.

According to the invention of claim 4, according to claim 1,
4. The control means according to claim 3, wherein the control means calculates a μ-sensitive gain based on a μ-sensitive gain map for obtaining a μ-sensitive gain based on the road surface friction coefficient estimated by the friction coefficient estimating means. The high-μ road basic steering wheel return current is calculated based on the vehicle speed sensitive steering wheel return map on the high-μ road using the rotational angular velocity. The control means calculates a low-μ road basic steering wheel return current based on the vehicle speed-sensitive steering wheel return map on the low μ road using the steering wheel rotational angular velocity at that time, and uses the μ-sensitive gain to return the steering wheel. The current is calculated by interpolation calculation, and the motor is controlled by the obtained handle return current.

According to the invention of claim 5, according to claim 1,
4. The control unit according to claim 3, wherein the control unit uses a plurality of vehicle speed-responsive steering wheel return maps created in advance for each of a plurality of road surface friction coefficients divided into a plurality of ranges, and the friction coefficient estimating unit from the map. Selects a map according to the estimated road surface friction coefficient, calculates the steering wheel return current,
The motor is controlled by the obtained steering wheel return current.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of an electric power steering device mounted on a four-wheel vehicle embodying the present invention will be described below with reference to FIGS.

FIG. 1 schematically shows an electric power steering apparatus. A steering wheel (steering handle) 1 drives a rack bar 4 via a steering shaft 2 and a steering gear box 3. A power unit 6 is drivingly connected to the steering shaft 2 via a gear reduction mechanism 5. The power unit 6
Has a motor 7. In the present embodiment, the motor 7 is constituted by a DC motor with a brush.

The steering shaft 2, the steering gear box 3, the rack bar 4, the gear reduction mechanism 5 and the like constitute a steering mechanism. The steering shaft 2 is provided with a torque sensor 9. The torque sensor 9 detects a steering torque generated when the steering wheel 1 is steered.

Next, an electric configuration of the electric power steering apparatus will be described. The electronic control unit (ECU 18) is equipped with ABS (antilock brake
ECU for controlling the brakes. A front wheel speed sensor 15 and a rear wheel speed sensor 17 are connected to the ECU 18. The front wheel speed sensor 15 outputs a pulse P1 having a cycle corresponding to the rotation speed of a front wheel (not shown) as an EC.
U18, and the rear wheel speed sensor 17 outputs to the ECU 18 a pulse P2 having a cycle corresponding to the rotation speed of the rear wheel (not shown).

The ECU 18 as the friction coefficient estimating means includes:
A pulse P1 from the front wheel speed sensor 15 and a pulse P2 from the rear wheel speed sensor 17 are input to calculate a road surface friction coefficient (hereinafter simply referred to as a friction coefficient) μ between the road surface and the tires when the vehicle is braking. ing.

More specifically, in the vehicle, the rotational speeds of the front wheels and the rear wheels differ according to the friction coefficient μ between the road surface and the tires during braking. At this time, the front wheel speed sensor 1
5 and the pulse P2 from the rear wheel speed sensor 17 are different from each other by the coefficient of friction μ between the road surface and the tire.
Is known to be correlated. ECU1
8 holds the friction coefficient μ calculated at the time of braking of the vehicle until a new friction coefficient μ is calculated at the time of the next braking.

Then, the ECU 18 outputs the coefficient of friction μ to the steering control device 19. The steering control device 19 includes an input port device 23 and an output port device 24. The input port device 23 includes a torque sensor 9, a front wheel speed sensor 15, and an electronic control unit (ECU).
18) are connected.

The torque sensor 9 outputs a voltage VT corresponding to a rotation torque (steering torque) T of the steering wheel 1 to a steering control device 19. Steering control device 19
Is a central processing unit (C) as control means and detection means.
PU) 20, a read-only memory (ROM) 21, and a read-only and write-only memory (RAM) 22 for temporarily storing data. This ROM 21 has a CP
A control program for causing the U20 to perform arithmetic processing is stored. This control program is stored in the RAM 22
The CPU 20 performs an arithmetic process based on the control program.

The ROM 21 stores a μ-sensitive gain K prepared in advance based on the μ-sensitive gain map shown in FIG.
(Μ) is stored. This μ-sensitive gain K (μ)
Is a function of the coefficient of friction μ. This μ-sensitive gain K
(Μ) takes a value from 0 to 1.

The ROM 21 stores a vehicle speed sensitive steering wheel return map (hereinafter, referred to as a first map) on a high μ road shown in FIG.
Of the high μ road basic steering wheel return current Id with respect to the steering wheel angular velocity ω at each vehicle speed V to be used when calculating
(Ω, V) is stored. The high μ road basic steering wheel return current Id (ω, V) is a function of the steering wheel angular velocity ω with the vehicle speed V as a parameter. The first map includes a high μ road reference angular velocity | ω0 |, and the high μ road reference angular velocity | ω0 |
Is the value of the handle rotation angular velocity ω at the point where the high μ road basic handle return current Id (ω, V) changes from 0. In addition,
In this embodiment, the steering wheel rotation angular velocity ω has a plus value when the steering wheel 1 is rotated rightward,
The angular velocity at the time of turning left is set to a negative value.
The range where the handlebar rotational angular velocity ω is −ω0 <ω <ω0 is regarded as a dead zone.

Further, the ROM 21 stores a vehicle speed sensitive steering wheel return map (hereinafter, referred to as a second map) on a low μ road shown in FIG. 5, and is used for obtaining a steering wheel return current I described later. The low-μ road basic steering wheel return current Is (ω, V) for the steering wheel angular velocity ω at the vehicle speed V is stored. The low μ road basic steering wheel return current Is (ω, V) is a function of the steering wheel angular velocity ω with the vehicle speed V as a parameter. The second map has a low μ road reference angular velocity | ω1 |, and this low μ road reference angular velocity | ω
1 | is a low μ road basic handle return current Is (ω, V) is 0
Is the value of the handle rotation angular velocity ω at a point that changes from. A range where the handlebar rotational angular velocity ω is −ω1 <ω <ω1 is regarded as a dead zone.

Then, as shown in FIG. 4 and FIG.
The maximum handle return current Is (ω, V) in the map is the handle return current Id in the first map.
The value is larger than the maximum current of (ω, V).

Further, the ROM 21 stores the μ-sensitive gain K (μ), the high-μ road basic handle return current Id (ω, V).
The following arithmetic expression for calculating the steering wheel return current I (μ, ω, V) is stored using the low μ road basic steering wheel return current Is (ω, V).

I (μ, ω, V) = K (μ) · Id (ω, V) + {1−K (μ)} · Is (ω, V) (1) High μ road basic handle return current Id (ω,
V) and the low μ road basic handle return current Is (ω, V).

The CPU 20 calculates a μ-sensitive gain K from the friction coefficient μ, the steering wheel angular velocity ω, and the vehicle speed V at that time.
(Μ), a high μ road basic handle return current Id (ω, V) and a low μ road basic handle return current Is (ω, V). Then, based on the obtained μ-sensitive gain K (μ), the high μ road basic handle return current Id (ω, V) and the low μ road basic handle return current Is (ω, V), the CPU 20 calculates The return current I (μ, ω, V) is obtained.

More specifically, if the friction coefficient μ is large on a high μ road while the vehicle is running, the μ-sensitive gain K (μ) has a large value, and thus {1-K (μ)} has a small value. Take. As a result, the first term of the handle return current I (μ, ω, V) takes a larger value than the second term. The larger the friction coefficient μ, the larger the value of the first term becomes than the value of the second term. That is, on the high μ road, the steering wheel return current I
The value of (μ, ω, V) greatly depends on the first term.

On the contrary, on the low μ road, the μ-sensitive gain K (μ) has a small value, and therefore {1-K (μ)} has a large value. As a result, the steering wheel return current I (μ,
The second term of (ω, V) takes a larger value than the first term. The smaller the friction coefficient μ, the further the second term is
It takes a value larger than the first term. That is, on the low μ road, the steering wheel return current I (μ, ω, V) greatly depends on the second term. That is, the value of the handle return current I (μ, ω, V) is high on a high μ road, and as the friction coefficient μ increases, the handle return current Id (ω, V) set on the high μ road and the μ-sensitive gain K ( μ), the lower the friction coefficient μ on the low μ road, the smaller the steering wheel return current Is (ω, V) and {1-K (μ)} Is governed by the value determined by the product of

The CPU 20 is connected to a circuit of the motor 7 for inputting a motor current Im flowing through the motor 7 and a motor terminal voltage Vm. The CPU 20 calculates the following based on the motor current Im and the motor terminal voltage Vm. Motor 7
Is calculated. In the present embodiment, the power unit 6, the gear reducer mechanism 5, and the motor 7 are connected so that the angular velocity of the motor 7 matches the steering wheel angular velocity ω. Therefore, calculating the angular velocity of the motor 7 is equivalent to calculating the steering wheel angular velocity ω.

Ω = {Vm− (R · Im + l · dIm / dt)} / Ke (2) where R is the resistance of the motor 7, L is the inductance of the motor 7, and Ke is the back electromotive force constant of the motor 7. , DIm / dt are differential values of the current Im of the motor 7.

The CPU 20 receives the pulse P1 from the front wheel speed sensor 15 and calculates the vehicle speed V. Furthermore, CP
U20 receives the friction coefficient μ from the ECU 18. Then, the CPU 20 reads the μ-sensitive gain K from the ROM 21.
(Μ), the handle return current Id (ω, V) and the handle return current Is (ω, V) are read into the RAM 22 and their values are calculated. Further, the CPU 20 reads the expression from the ROM 21 into the RAM 22 and stores the μ-sensitive gain K
(Μ), the value of the handle return current I (μ, ω, V) is calculated based on the values of the handle return current Id (ω, V) and the handle return current Is (ω, V).

The CPU 20 calculates the steering wheel return current I (μ,
ω, V) is output to the motor drive circuit 25 via the output port device 24, and the motor drive circuit 25 sends the corresponding steering wheel return current I (μ, ω, V) to the motor 7 based on the value. Output. The motor 7 receives the steering wheel return current I (μ, ω, V) and inputs the steering wheel return current I
The steering wheel return force F proportional to (μ, ω, V) is output.

(Operation of the First Embodiment) Next, the CPU in the operation of the electric power steering apparatus constructed as described above will be described.
20 will be described with reference to the flowchart of FIG. This flowchart is periodically executed by interruption.

First, in step (hereinafter referred to as step S) 1, the friction coefficient μ from the ECU 18, the pulse P from the front wheel vehicle speed sensor 15, the voltage VT from the torque sensor 9, the motor current Im and the motor terminal voltage Vm Is read into the RAM 22.

In S2, the steering torque T is calculated based on the voltage VT from the torque sensor 9. Also, S2
In the above, the input motor current Im and the motor terminal voltage Vm are used to calculate the steering wheel angular velocity ω based on the above equation (2).

In S3, the steering torque T obtained in S2
Is determined based on the steering wheel rotational angular velocity ω. That is, when the steering torque T is 0 (or almost 0) and the motor 7 is rotating, that is, when the steering wheel angular velocity ω is a finite value, it is determined that the steering wheel is in the returning state, and when not. Is determined not to be in the state of returning the steering wheel.

If it is determined in S3 that the steering wheel is not in the returning state, the flow shifts to S7, where other processing is performed, and then this flowchart is temporarily ended. In S3, if it is determined that the steering wheel is in the returning state, the process proceeds to S4.

In S4, the CPU 20 calculates the vehicle speed V based on the pulse P1 from the front wheel vehicle speed sensor 15.
Next, in S4, the CPU 20 determines the input friction coefficient μ.
Is used to determine the μ-sensitive gain K (μ) based on the μ-sensitive gain map. In the next S5, the vehicle speed V and the steering wheel angular velocity ω are used to determine the high μ road basic steering wheel return current Id (ω, V) based on the first map. Further, the vehicle speed V and the steering wheel angular velocity ω
Is used to determine the low μ road basic handle return current Is (ω, V) based on the second map. Also, the μ-sensitive gain K (μ), the calculated high μ road basic handle return current I
d (ω, V) and low μ road basic handle return current Is
Using (ω, V), the steering wheel return current I (μ, ω, V) is calculated based on the above equation (1).

At S6, the steering wheel return current I
The value of (μ, ω, V) is output to the motor driving device 25.
The motor 7 outputs a steering wheel return force F corresponding to the steering wheel return current I (μ, ω, V), and once ends the control routine.

Therefore, the motor 7 is driven according to the coefficient of friction μ.
When the friction coefficient μ is large, the small handle return force F
When the friction coefficient μ is small, a large steering wheel return force F can be output.

Next, the features of this embodiment will be described below. (1) In the above embodiment, the CPU 20 determines the steering wheel return current I according to the friction coefficient μ between the road surface and the tire.
(Μ, ω, V), and the value of the steering wheel return current I (μ, ω, V) increases as the friction coefficient μ decreases, and decreases as the friction coefficient μ increases. Since the motor 7 inputs a current based on the value of the steering wheel return current I (μ, ω, V) from the motor drive circuit 25, when the friction coefficient μ is large according to the friction coefficient μ, the motor 7 responds. When the frictional coefficient μ is small, a small steering wheel return force F can be output.

Therefore, the operator of the vehicle, when traveling at low speed on a low μ road such as a fresh snow road, a snowy road, or a frozen road in a cold region, for example, causes the steering wheel rotation angular speed ω to exceed the low μ road reference angular speed | ω1 | The steering wheel return force F increases in accordance with the decrease in the friction coefficient μ, so that the steering wheel (steering handle) 1 can be returned to a good steering characteristic after being steered.

Also, the driver of the vehicle must be on a dry road having a high μ.
Steering wheel rotational angular velocity ω is high μ road reference angular velocity | ω0
Exceeds |, the steering wheel return force F decreases in accordance with the increase in the friction coefficient μ. Therefore, after steering the steering wheel (steering handle) 1,
Vibration that swings or returns to the opposite side beyond the neutral position is prevented, and the handle can be returned easily.

(2) In this embodiment, the CPU 20 calculates the steering wheel rotational angular velocity ω based on the above equation (2) using the input motor current Im and the motor terminal voltage Vm. . As a result, a detection sensor for detecting the handle rotation angular velocity is not required, and the manufacturing cost can be reduced.

(3) In the present embodiment, the CPU (control means) 20 calculates the μ-sensitive gain based on the μ-sensitive gain map based on the friction coefficient estimated by the ECU (friction coefficient estimating means) 18 (μ). (Corresponds to sensitive gain calculating means),
A high-μ road basic handle return current is calculated based on the first map using the handle rotational angular velocity ω at that time (corresponding to a high μ road basic handle return current calculation means), and the handle rotational angular velocity ω at that time is used. Based on the second map, a low- [mu] road basic handle return current is calculated (corresponding to low- [mu] road basic handle return current calculation means), and a [mu] sensitive gain is used to calculate the handle return current by interpolation. (Corresponding to the handle return current calculation means). And
The motor 7 is controlled by the obtained handle return current.

As a result, the steering wheel return current can be calculated by the interpolation calculation, and the storage capacity of the ROM 21 for storing the map can be reduced. (Second Embodiment) Next, a second embodiment will be described with reference to FIGS.
This will be described with reference to FIG.

The electric power steering apparatus according to the present embodiment has a μ-sensitive gain K (μ) prepared in advance based on the μ-sensitive gain map of the first embodiment, and the first power setting on a high μ road.
The high- [mu] road basic handle return current Id ([omega], V) prepared based on the map, and the low [mu] road basic handle return current Is prepared based on the second map on the low [mu] road.
A difference from the first embodiment is that a plurality of vehicle speed sensitive steering wheel return maps described later are stored in the ROM 21 instead of (ω, V).

In the first embodiment, the motor 7 is constituted by a brushed DC motor, and the CPU 20 calculates the motor current Im flowing through the motor 7 and the motor terminal voltage Vm from the equation (2) based on the equation (2). The handle rotation angular velocity (motor angular velocity) was calculated.

In this embodiment, the motor 7 is constituted by a brushless DC motor instead, and a rotation angle sensor 10 for detecting a handle rotation angle necessary for detecting a motor angular velocity (handle rotation angular velocity) ω is shown in FIG. The difference from the first embodiment is that the motor 7 is provided on the motor 7 as shown in FIG.

The other hardware configuration has the same configuration as that of the first embodiment or a configuration corresponding thereto, and therefore detailed description thereof is omitted. The vehicle speed sensitive steering wheel return map includes a high μ vehicle speed sensitive steering wheel return map (hereinafter referred to as a high μ map) shown in FIG. 10A, and a high / middle vehicle speed sensitive steering wheel return map (hereinafter referred to as high / middle μ) shown in FIG. 10B. 10), a low / middle μ vehicle speed sensitive steering wheel return map (hereinafter referred to as a “low / middle μ map”) shown in FIG.
A low-μ vehicle speed-sensitive steering wheel return map shown in FIG.
(Referred to as a low μ map).

These vehicle speed sensitive steering wheel return maps are as follows:
Four ranges of friction coefficient μ from the larger one, namely high μ,
It is divided into high-medium μ, low-medium μ, and low μ, and is provided for each friction coefficient μ. In the present embodiment, the range of the friction coefficient μ at the time of the high μ is 0.75 to 1.0, and the range of the friction coefficient μ at the time of the high μ is 0.5 to 0.75, and the range of the low μ The range of the friction coefficient μ is 0.25 to 0.5, and the range of the friction coefficient μ when the friction coefficient is low is 0.0 to 0.25.

The high μ map, the high middle μ map, the low middle μ map, and the low μ map store the steering wheel return current I (ω, V) with respect to the steering wheel angular velocity ω at each vehicle speed V. The steering wheel return current I (ω, V) is a function of the steering wheel angular velocity ω with the vehicle speed V as a parameter. In each map, the respective reference rotational angular velocities (= ωa>ωb>ωc> ωd) are set to different values, and the slope (or the falling) rises from the point where the steering wheel return current I (ω, V) changes from 0. The slope is set to be steeper as the friction coefficient is lower on the μ side.

As shown in FIGS. 10 (a) to 10 (d), when the vehicle speed V at that time is the same, the steering wheel return current becomes larger as the map on the low μ map side increases. The current is set to be large.

Therefore, the ROM 21 stores four types of steering wheel return currents I (ω, V) prepared in advance based on the four vehicle speed sensitive steering wheel return maps. ROM
21 stores a control program for calculating and outputting the steering wheel return current I (ω, V) using the four types of maps and controlling the motor 7.

(Operation of the Second Embodiment) Next, the CPU in the operation of the electric power steering apparatus constructed as described above will be described.
20 will be described with reference to the flowcharts of FIGS.

In this embodiment, the flowchart of FIG. 8 is different from the routine executed at a predetermined cycle in the CP.
U21 is the steering torque T input from the torque sensor 9.
It is determined whether or not the steering wheel returns based on the steering wheel rotational angle ω calculated based on the steering wheel rotation angle input from the rotation angle sensor 10, and an interrupt routine executed when the steering wheel return is determined. is there. That is, when the steering torque T is 0 (or almost 0) and the motor 7 is rotating, that is, the steering wheel rotational angular velocity ω
Is executed, when it is determined that the handle is in the return state, when is a finite value.

First, at step 11, the CPU 20 reads the friction coefficient μ from the ECU 18, the pulse P from the front wheel speed sensor 15, and the detection signal value from the rotation angle sensor 10 into the RAM 22.

In step 12, the vehicle speed V is calculated based on the pulse P 1 from the front wheel vehicle speed sensor 15, and the steering wheel 1 of the steering wheel 1 is calculated based on the detection value (the steering wheel rotation angle) from the rotation angle sensor 10. Calculate the rotational angular velocity ω.

CPU 20 performs a motor current calculation in step 12. FIG. 8 shows the processing routine in step 12, which constitutes the handle return map selection means of the present invention. In S120, the steering wheel return current I (ω, V) of the vehicle speed sensitive steering wheel return map in the range to which the friction coefficient μ belongs is stored in the ROM 21.
From the RAM 22.

Then, the CPU 20 executes S121 to S124.
In any one of the steps, the steering wheel return current I is calculated based on the steering wheel angular velocity ω and the vehicle speed V.
The value of (ω, V) is calculated.

In step 13, the CPU 20 sets the value of the steering wheel return current I (ω, V) to the motor drive circuit 25.
Output to Now, for example, when the vehicle is running on a high μ road (μ =
0.76), when the steering wheel is steered and the motor angular velocity (handle rotational angular velocity) exceeds the reference angular velocity ωa, the CPU 20 inputs the friction coefficient μ from the ECU 18 at this time, and the friction coefficient μ The handle return current I (ω, V) of the high μ map in the range to which
Read in AM22. Then, the CPU 20 calculates the steering wheel return current I (ω, V). Then, the CPU 20 outputs the value to the motor drive circuit 25. The motor drive circuit 25 supplies a current corresponding to the value to the motor 7. The motor 7 outputs a steering wheel return force F corresponding to the value.

Further, when the vehicle is running at a vehicle speed V, a low-medium μ road (μ
0.4), when the motor angular velocity (handle rotation angular velocity) exceeds the reference angular velocity ωc, the CPU 20 inputs the friction coefficient μ from the ECU 18 at this time, The handle return current I (ω, V) of the μ map is read from the ROM 21 to the RAM 22. Then, the CPU 20 outputs the steering wheel return current I (ω,
V) is calculated. Then, the CPU 20 outputs the value to the motor drive circuit 25. The motor drive circuit 25 supplies a current corresponding to the value to the motor 7. The motor 7 outputs a steering wheel return force F corresponding to the value.

Therefore, the motor 7 is driven by the friction coefficient μ
When the friction coefficient μ is large, a small handle return force F can be output, and when the friction coefficient μ is small, a large handle return force F can be output.

The embodiments of the present invention are not limited to the above embodiments, but may be modified as follows. In the second embodiment, the motor angular velocity (handle rotation angular velocity) ω is calculated based on the detection value of the rotation angle sensor 10 as C
Although the PU 20 performs the calculation, a rotation position sensor for detecting the rotation position of the motor 7 may be provided, and the CPU 20 may calculate and obtain the steering wheel rotation angular speed based on the position detection.

In the second embodiment, four maps are selected in accordance with the friction coefficient μ, but may be two, three, or five or more. Next, technical ideas other than the inventions described in the claims that can be grasped from the embodiment and other examples will be described below together with their effects.

(1) The friction coefficient estimating means includes an ABS
5. An ECU that controls the system.
The electric power steering apparatus according to any one of the above items. By doing so, the road surface friction coefficient can be estimated by the ABS (antilock brake system) ECU, so that it is not necessary to separately provide another ECU, and the cost can be reduced. The ECU 18 of the first embodiment and the second embodiment corresponds to the ECU in this case.

(2) The detection means inputs the motor current Im flowing through the motor and the motor terminal voltage Vm, and calculates the angular velocity of the motor from the motor current Im and the motor terminal voltage Vm. The electric power steering apparatus according to any one of claims 1 to 5. This eliminates the need for a rotation angle sensor, reduces the number of components, and reduces costs.

[0076]

As described above in detail, according to the first to fifth aspects, a good handle return property can be obtained on both a low .mu. Road and a high .mu. Road. Good performance. The same, that is, optimal steering wheel return property can be obtained on the high μ road and the low μ road.

According to the third aspect of the present invention, in addition to the effects of the first or second aspect, another sensor for detecting the steering wheel angular velocity is not required, and the cost can be reduced.

According to the fourth aspect of the present invention, in addition to the effects of any one of the first to third aspects, interpolation calculation
The steering wheel return current can be calculated, and the storage capacity of the ROM for storing the map is small.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electric power steering device according to a first embodiment of the present invention.

FIG. 2 is an electrical configuration diagram of the electric power steering device.

FIG. 3 is a μ-sensitive gain map according to the embodiment.

FIG. 4 is a vehicle speed sensitive steering wheel return map also set on a high μ road.

FIG. 5 is a vehicle speed sensitive steering wheel return map also set on a low μ road.

FIG. 6 is a flowchart illustrating a processing operation of a CPU according to the first embodiment.

FIG. 7 is a schematic diagram of an electric power steering device according to a second embodiment.

FIG. 8 is a flowchart illustrating a processing operation of a CPU according to the second embodiment.

FIG. 9 is a flowchart illustrating a processing operation of the CPU.

FIG. 10 is a high μ vehicle speed sensitive steering wheel return map in the second embodiment, (b) is a high / middle μ vehicle speed sensitive steering wheel return map, (c) is a low / middle μ vehicle speed sensitive steering wheel return map,
(D) is a low μ vehicle speed sensitive steering wheel return map.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering gear box, 4 ... Rack bar,
5. Gear reduction mechanism (a steering mechanism is constituted by the steering shaft 2, the steering gear box 3, the rack bar 4, the gear reduction mechanism 5, and the like). 7 ... motor, 9 ... torque sensor, 10 ... rotational angular velocity sensor, 1
5 front wheel speed sensor, 18 ECU (constituting friction coefficient estimating means), 19 steering control device, 20 CPU
(Constituting the control means and the detection means), 25 ... motor drive circuit.

Continued on front page F term (reference) 3D032 CC05 CC48 DA03 DA09 DA15 DA24 DA63 DA64 DA65 DA82 DB02 DB03 DC03 DC08 DC22 DC35 DD02 DD06 DD17 EA01 EB11 EC23 FF01 GG01 3D033 CA03 CA11 CA13 CA16 CA19 CA20 CA21

Claims (5)

[Claims] 1. A motor for calculating a steering wheel return force based on at least a steering wheel rotational angular velocity generated by operation of a steering shaft and a vehicle speed, and applying a steering wheel return force to a steering mechanism based on the calculation result. An electric power steering apparatus comprising a control means for controlling an output, comprising: a friction coefficient estimating means for estimating a road surface friction coefficient of a running road during traveling, wherein the control means comprises a road surface friction coefficient estimated by the friction coefficient estimating means. The electric motor is characterized in that the current output value to the motor is increased so that the steering wheel return force is increased on the low μ road side with a low road friction coefficient than on the high μ road side with a high road friction coefficient. Power steering device. 2. A motor for calculating a steering wheel return force based on at least a steering wheel rotation angular velocity generated by operation of a steering shaft and a vehicle speed, and applying a steering wheel return force to a steering mechanism based on the calculation result. An electric power steering apparatus provided with control means for controlling an output, comprising: a friction coefficient estimating means for estimating a road surface friction coefficient of a running road during traveling, wherein the control means comprises a plurality of handles corresponding to the magnitude of the friction coefficient. Having a return map and based on these handle return maps,
According to the road friction coefficient estimated by the friction coefficient estimating means, the current output to the motor is set so as to increase the steering wheel return force on the low μ road side where the road friction coefficient is low than on the high μ road side where the road friction coefficient is high. An electric power steering device characterized by increasing the value. 3. The electric power steering apparatus according to claim 1, further comprising a detection unit configured to detect a steering wheel angular velocity generated due to an operation of the steering shaft. 4. The control means calculates a μ-sensitive gain based on a μ-sensitive gain map that obtains a μ-sensitive gain based on the road surface friction coefficient estimated by the friction coefficient estimating means, and uses a steering wheel angular velocity at that time. The basic steering wheel return current on the high μ road is calculated based on the vehicle speed sensitive steering wheel return map on the high μ road, and the low μ based on the vehicle speed sensitive steering wheel return map on the low μ road using the steering wheel angular velocity at that time. 4. The method according to claim 1, wherein a road basic steering wheel return current is calculated, the steering wheel return current is calculated by interpolation using the μ-sensitive gain, and the motor is controlled by the obtained steering wheel return current. The electric power steering device according to any one of the above. 5. The control means uses a plurality of vehicle speed sensitive steering wheel return maps prepared in advance for each of a plurality of divided road surface friction coefficients, and the road surface estimated by the friction coefficient estimating means from the map. 2. A steering wheel return map selecting means for selecting a map according to a friction coefficient, wherein a steering wheel return current is calculated from the selected steering wheel return map, and the motor is controlled by the obtained steering wheel return current. An electric power steering apparatus according to claim 3.